CVE-2022-39957: Response body bypass in OWASP ModSecurity Core Rule Set via a specialy crafted charset in the HTTP Accept header

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% 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-693

Description

The OWASP ModSecurity Core Rule Set (CRS) is affected by a response body bypass. A client can issue an HTTP Accept header field containing an optional "charset" parameter in order to receive the response in an encoded form. Depending on the "charset", this response can not be decoded by the web application firewall. A restricted resource, access to which would ordinarily be detected, may therefore bypass detection. 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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