CVE-2026-21876
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network without logging in. High risk of data exposure.
- Exploit odds
- 17.3% chance of exploitation in the next 30 days (EPSS). Higher than most.
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 17.3% in the next 30 days (EPSS).
- Severity: 9.3 CRITICAL (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 17.3% · EPSS, next 30 days
- Weakness
- CWE-794
- Record status
- Modified
Affected
- Owasp Modsecurity Core Rule Set < 3.3.8
- Owasp Modsecurity Core Rule Set < 4.22.0
Attack profile CVSS 3.1 · 9.3
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-21876.md and follow it. Check whether this project is affected by CVE-2026-21876. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83
- https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6
- https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8
- https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5
References
- https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83
- https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6
- https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8
- https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5
- https://github.com/daytriftnewgen/CVE-2026-21876