CVE-2024-38475: Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path.

[Eric Covener <covener () apache org>]

Severity: important

Affected versions:

- Apache HTTP Server 2.4.0 through 2.4.59

Description:

Improper escaping of output in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows an attacker to map URLs to 
filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any 
URL, resulting in code execution or source code disclosure. 

Substitutions in server context that use a backreferences or variables as the first segment of the substitution are 
affected.  Some unsafe RewiteRules will be broken by this change and the rewrite flag "UnsafePrefixStat" can be used to 
opt back in once ensuring the substitution is appropriately constrained.

Credit:

Orange Tsai (@orange_8361) from DEVCORE (finder)

References:

https://httpd.apache.org/security/vulnerabilities_24.html
https://httpd.apache.org/
https://www.cve.org/CVERecord?id=CVE-2024-38475

Timeline:

2024-04-01: reported