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Apache mod_security: Rule bypass


1.  Gentoo Linux Security Advisory

Version Information

Advisory Reference GLSA 200705-17 / mod_security
Release Date May 17, 2007
Latest Revision December 30, 2007: 02
Impact low
Exploitable remote
Package Vulnerable versions Unaffected versions Architecture(s)
www-apache/mod_security < 2.1.1 >= 2.1.1 All supported architectures

Related bugreports: #169778


A vulnerability has been discovered in mod_security, allowing a remote attacker to bypass rules.

2.  Impact Information


mod_security is an Apache module designed for enhancing the security of the Apache web server.


Stefan Esser discovered that mod_security processes NULL characters as terminators in POST requests using the application/x-www-form-urlencoded encoding type, while other parsers used in web applications do not.


A remote attacker could send a specially crafted POST request, possibly bypassing the module ruleset and leading to the execution of arbitrary code in the scope of the web server with the rights of the user running the web server.

3.  Resolution Information


There is no known workaround at this time.


All mod_security users should upgrade to the latest version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose ">=www-apache/mod_security-2.1.1"

4.  References


Page updated May 17, 2007

Summary: This is a Gentoo Linux Security Advisory

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