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Vulnerability record · CVE-2026-21876 · published 8 January 2026

CVE-2026-21876: Owasp modsecurity core rule set vulnerability

Owasp · Owasp Modsecurity Core Rule Set

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.

5.3 CVSS 3.1 Medium EPSS 18% · top 3.0% CWE-794 · CWE-794
5.3CVSS 3.1 base score
18%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References, 1 tagged exploit
17 Jun 2026Last modified by NVD

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/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83 Patch
https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6 Patch
https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8 ProductRelease Notes
https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0 ProductRelease Notes
https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5 ExploitVendor Advisory
https://github.com/daytriftnewgen/CVE-2026-21876

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2022-39955Owasp modsecurity core rule set incorrect authorization vulnerabilityThe OWASP ModSecurity Core Rule Set (CRS) is affected by a partial rule set bypass by submitting a specially crafted HTTP Content-Type header field t…EPSS 1.4%9.8CVE-2022-39956Owasp modsecurity core rule set incorrect authorization vulnerabilityThe OWASP ModSecurity Core Rule Set (CRS) is affected by a partial rule set bypass for HTTP multipart requests by submitting a payload that uses a ch…EPSS 1.2%9.8CVE-2020-22669Owasp modsecurity core rule set sql injection vulnerabilityModsecurity owasp-modsecurity-crs 3.2.0 (Paranoia level at PL1) has a SQL injection bypass vulnerability. Attackers can use the comment characters an…EPSS 1.3%9.8CVE-2021-35368Owasp modsecurity core rule set vulnerabilityOWASP ModSecurity Core Rule Set 3.1.x before 3.1.2, 3.2.x before 3.2.1, and 3.3.x before 3.3.2 is affected by a Request Body Bypass via a trailing pa…EPSS 2.7%7.5CVE-2026-33691Owasp modsecurity core rule set vulnerabilityThe OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 3.3.9 a…EPSS 1.6%7.5CVE-2022-39957Owasp modsecurity core rule set vulnerabilityThe OWASP ModSecurity Core Rule Set (CRS) is affected by a response body bypass. A client can issue an HTTP Accept header field containing an optiona…EPSS 0.99%7.5CVE-2022-39958Owasp modsecurity core rule set incorrect authorization vulnerabilityThe OWASP ModSecurity Core Rule Set (CRS) is affected by a response body bypass to sequentially exfiltrate small and undetectable sections of data by…EPSS 1.2%7.5CVE-2018-16384Owasp modsecurity core rule set sql injection vulnerabilityA SQL injection bypass (aka PL1 bypass) exists in OWASP ModSecurity Core Rule Set (owasp-modsecurity-crs) through v3.1.0-rc3 via {`a`b} where a is a …EPSS 1.7%

Source: NIST National Vulnerability Database (record CVE-2026-21876), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.