ModSecurity before 2.5.11 treats request parameter values containing single quotes as files, which allows remote attackers to bypass filtering rules and perform other attacks such as cross-site scripting (XSS) attacks via a single quote in a request parameter in the Content-Disposition field of a request with a multipart/form-data Content-Type header.
http://www.suspekt.org/downloads/POC2009-ShockingNewsInPHPExploitation.pdf
http://www.securityfocus.com/bid/54156
http://www.openwall.com/lists/oss-security/2012/06/22/2
http://www.openwall.com/lists/oss-security/2012/06/22/1
http://secunia.com/advisories/49576
http://lists.opensuse.org/opensuse-updates/2013-08/msg00031.html
http://lists.opensuse.org/opensuse-updates/2013-08/msg00025.html
http://lists.opensuse.org/opensuse-updates/2013-08/msg00020.html
http://blog.ivanristic.com/2012/06/modsecurity-and-modsecurity-core-rule-set-multipart-bypasses.html