In ModSecurity before 2.9.6 and 3.x before 3.0.8, HTTP multipart requests were incorrectly parsed and could bypass the Web Application Firewall. NOTE: this is related to CVE-2022-39956 but can be considered independent changes to the ModSecurity (C language) codebase.

The OWASP ModSecurity Core Rule Set (CRS) is affected by a partial rule set bypass for HTTP multipart requests by submitting a payload that uses a character encoding scheme via the Content-Type or the deprecated Content-Transfer-Encoding multipart MIME header fields that will not be decoded and inspected by the web application firewall engine and the rule set. The multipart payload will therefore bypass detection. A vulnerable backend that supports these encoding schemes can potentially be exploited. The legacy CRS versions 3.0.x and 3.1.x are affected, as well as the currently supported versions 3.2.1 and 3.3.2. Integrators and users are advised upgrade to 3.2.2 and 3.3.3 respectively. The mitigation against these vulnerabilities depends on the installation of the latest ModSecurity version (v2.9.6 / v3.0.8).