Critical
modsecurity-crs — security advisory
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.
- Products
- modsecurity-crs
- Affected versions
- 2.2.9-1, 3.0.0-3, 3.0.2-1, 3.1.1-1, 3.2.0-1, 3.3.0-1, 3.3.2-1, 3.3.5-1, 3.3.5-2, 3.3.7-1, 3.3.8-1, 3.3.9-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-21876
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:56 UTC · Revision 1
Source evidence
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.
osv:UBUNTU-CVE-2026-21876
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
modsecurity-crs
Fixed versions: Not specified
Complete source record
{
"id": "ef122be2cc8de69057e63d40b90521147d0f546c5ffe47737e4f821e7de0e68c",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-21876",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-21876",
"summary": "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.",
"evidence": "osv:UBUNTU-CVE-2026-21876",
"products": [
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.2.9-1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.0.0-3",
"evidence": "/affected/1/versions"
},
{
"value": "3.0.2-1",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.1.1-1",
"evidence": "/affected/2/versions"
},
{
"value": "3.2.0-1",
"evidence": "/affected/2/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.0-1",
"evidence": "/affected/3/versions"
},
{
"value": "3.3.2-1",
"evidence": "/affected/3/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/4/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.5-1",
"evidence": "/affected/4/versions"
},
{
"value": "3.3.5-2",
"evidence": "/affected/4/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.7-1",
"evidence": "/affected/5/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/6/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.8-1",
"evidence": "/affected/6/versions"
},
{
"value": "3.3.9-1",
"evidence": "/affected/6/versions"
}
]
},
{
"name": {
"value": "modsecurity-crs",
"evidence": "/affected/7/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.7-1",
"evidence": "/affected/7/versions"
},
{
"value": "3.3.8-1",
"evidence": "/affected/7/versions"
}
]
}
],
"severity": "critical",
"structured": {
"id": "UBUNTU-CVE-2026-21876",
"aliases": [
"UBUNTU-CVE-2026-21876"
],
"metrics": [
{
"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"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=xenial",
"ecosystem": "Ubuntu:16.04:LTS"
},
"versions": [
"2.2.9-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "2.2.9-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=bionic",
"ecosystem": "Ubuntu:18.04:LTS"
},
"versions": [
"3.0.0-3",
"3.0.2-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.0.2-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"3.1.1-1",
"3.2.0-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.2.0-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"3.3.0-1",
"3.3.2-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.3.2-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=noble",
"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"3.3.5-1",
"3.3.5-2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.3.5-2"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
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}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=questing",
"ecosystem": "Ubuntu:25.10"
},
"versions": [
"3.3.7-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.3.7-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=stonking",
"ecosystem": "Ubuntu:26.10"
},
"versions": [
"3.3.8-1",
"3.3.9-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.3.9-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "modsecurity-crs",
"purl": "pkg:deb/ubuntu/modsecurity-crs?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"3.3.7-1",
"3.3.8-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-21876.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "modsecurity-crs",
"binary_version": "3.3.8-1"
}
]
}
}
],
"modified": "2026-10-17T12:59:54.834100258Z",
"provider": "osv",
"upstream": [
"CVE-2026-21876"
],
"references": [
"https://ubuntu.com/security/CVE-2026-21876",
"https://www.cve.org/CVERecord?id=CVE-2026-21876",
"https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5",
"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"
]
},
"related_cves": [
{
"value": "CVE-2026-21876",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 359942,
"published_at": "2026-01-08T14:15:00+00:00"
}