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Apache mod_rewrite Buffer Overflow Vulnerability
Jul 28 2006 02:50PM
Avert avertlabs com
McAfee Avert(tm) Labs Security Advisory
Public Release Date: 2006-07-09
Apache 1.3.29/2.X mod_rewrite Buffer Over Vulnerability
Mod_rewrite is an Apache module that can be used to remap requests
based on regular expression matches of the requested URI. A buffer
overflow vulnerability exists when dealing with rewritten URI's that
are prefixed with the LDAP protocol scheme.
Exploitation leads to remote access to the vulnerable machine and
therefore the risk factor is critical.
* Vulnerable Systems
Apache 2.0.x/mod_rewrite - only 2.0.46 and higher are vulnerable
* Vulnerability Information
The mod_rewrite module contains an off-by-one buffer overflow
vulnerability when escaping an absolute URI scheme. The vulnerability
occurs within escape_absolute_uri( ) when separating out tokens
within an LDAP URL. Triggering the vulnerability results in a pointer
to user-controlled data to be written outside of the bounds of a
character pointer array, which in many cases can be used to gain
complete control of the affected host.
Note that an LDAP-specific rule does not need to be exist to exploit
the vulnerability. However, a rule must exist with the following
- A rule must exist where the user can control the initial part of the rewritten URL
- The rule must not contain a forbidden or gone flag [F or G]
- Rules with "noescape" [NE] flag settings are not affected.
This vulnerability was discovered by Mark Dowd of McAfee Avert Labs.
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