CVE-2022-39955: Partial rule set bypass in OWASP ModSecurity Core Rule Set by submitting a specially crafted HTTP Content-Type header

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2022-09-20 · updated 2026-06-17
Weakness: CWE-863

Description

The OWASP ModSecurity Core Rule Set (CRS) is affected by a partial rule set bypass by submitting a specially crafted HTTP Content-Type header field that indicates multiple character encoding schemes. A vulnerable back-end can potentially be exploited by declaring multiple Content-Type "charset" names and therefore bypassing the configurable CRS Content-Type header "charset" allow list. An encoded payload can bypass CRS detection this way and may then be decoded by the backend. 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 to upgrade to 3.2.2 and 3.3.3 respectively.

Affected products

Debian Linux: 10.0
Fedoraproject Fedora: 35, 36, 37
coreruleset: from 3.0.0 before 3.2.2; from 3.3.0 before 3.3.3 — fixed in 3.2.2, 3.3.3

How to fix

Upgrade to a fixed version: coreruleset 3.2.2, 3.3.3. Check the vendor advisory for mitigations.

References

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