CVE-2026-21876
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.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 14.2%, higher than 96% of all known CVEs. Patch or mitigate before the next change window.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- EPSS
- 14.22% probability · 96th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-794
- Affected
- owasp/owasp modsecurity core rule set
- Source
- security-advisories@github.com
References
- https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83Patch
- https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6Patch
- https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8Product, Release Notes
- https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0Product, Release Notes
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5Exploit, Vendor Advisory
- https://github.com/daytriftnewgen/CVE-2026-21876
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.