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CVE-2026-21876

9.3 · CRITICAL

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls.

Published Jan 8, 2026CWE-794EPSS 17.88%

Overview

CVE-2026-21876 is a critical-severity vulnerability. It was published on January 8, 2026 and has a CVSS 3.1 base score of 9.3 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.3, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83GitHubgithub.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6GitHubgithub.com/coreruleset/coreruleset/releases/tag/v3.3.8GitHubgithub.com/coreruleset/coreruleset/releases/tag/v4.22.0GitHubgithub.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5GitHubgithub.com/daytriftnewgen/CVE-2026-21876

How CyberStrike helps

Frequently asked questions

What is CVE-2026-21876?

CVE-2026-21876 is a critical-severity vulnerability. It was published on January 8, 2026 and has a CVSS 3.1 base score of 9.3 (CRITICAL).

How severe is CVE-2026-21876?

This vulnerability has a CVSS 3.1 base score of 9.3, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-21876?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-21876?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-21876 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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