{"id":"UBUNTU-CVE-2026-21876","details":"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.","modified":"2026-03-19T10:32:58.677223Z","published":"2026-01-08T14:15:00Z","upstream":["CVE-2026-21876"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-21876"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-21876"},{"type":"REPORT","url":"https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5"},{"type":"REPORT","url":"https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83"},{"type":"REPORT","url":"https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6"},{"type":"REPORT","url":"https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8"},{"type":"REPORT","url":"https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0"}],"affected":[{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/modsecurity-crs@2.2.9-1?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.9-1"],"ecosystem_specific":{"binaries":[{"binary_version":"2.2.9-1","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}},{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/modsecurity-crs@3.0.2-1?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.0-3","3.0.2-1"],"ecosystem_specific":{"binaries":[{"binary_version":"3.0.2-1","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}},{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/modsecurity-crs@3.2.0-1?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.1-1","3.2.0-1"],"ecosystem_specific":{"binaries":[{"binary_version":"3.2.0-1","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}},{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/modsecurity-crs@3.3.2-1?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.3.0-1","3.3.2-1"],"ecosystem_specific":{"binaries":[{"binary_version":"3.3.2-1","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}},{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/modsecurity-crs@3.3.5-2?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.3.5-1","3.3.5-2"],"ecosystem_specific":{"binaries":[{"binary_version":"3.3.5-2","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}},{"package":{"name":"modsecurity-crs","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/modsecurity-crs@3.3.7-1?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.3.7-1"],"ecosystem_specific":{"binaries":[{"binary_version":"3.3.7-1","binary_name":"modsecurity-crs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},{"type":"Ubuntu","score":"medium"}]}