HighFix available
expat — security advisory
Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.
- Products
- expat
- Affected versions
- 2.5.0-1, 2.5.0-1+deb12u1, 2.5.0-1+deb12u2, 2.5.0-1+deb12u3, 2.7.1-2, 2.7.2-1, 2.7.3-1, 2.7.3-2, 2.7.4-1, 2.7.5-1, 2.8.0-1, 2.8.0-2, 2.8.1-1, 2.8.2-1, 2.8.2-1~deb13u1, 2.8.3-1, 2.8.3-1~deb13u1, 2.8.4-1, 2.8.4-2, 2.8.5-1, 2.8.5-2
- Fixed versions
- 2.5.0-1+deb12u4, 2.8.4-1, 2.9.0-1~deb13u1
- CVEs
- CVE-2026-66046
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 22:59 UTC · Revision 1
Source evidence
Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.
osv:DEBIAN-CVE-2026-66046
expat
Fixed versions: 2.5.0-1+deb12u4
expat
Fixed versions: 2.9.0-1~deb13u1
expat
Fixed versions: 2.8.4-1
Complete source record
{
"id": "fb230fc1efa6088bf5b6a04d2dd834e3b6e6fb28365b0f968e4bf5530ccdab02",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-66046",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-66046",
"summary": "Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.",
"evidence": "osv:DEBIAN-CVE-2026-66046",
"products": [
{
"name": {
"value": "expat",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "2.5.0-1+deb12u4",
"evidence": "/affected/0/ranges"
}
],
"affected_versions": [
{
"value": "2.5.0-1",
"evidence": "/affected/0/versions"
},
{
"value": "2.5.0-1+deb12u1",
"evidence": "/affected/0/versions"
},
{
"value": "2.5.0-1+deb12u2",
"evidence": "/affected/0/versions"
},
{
"value": "2.5.0-1+deb12u3",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "expat",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "2.9.0-1~deb13u1",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": [
{
"value": "2.7.1-2",
"evidence": "/affected/1/versions"
},
{
"value": "2.7.2-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.7.3-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.7.3-2",
"evidence": "/affected/1/versions"
},
{
"value": "2.7.4-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.7.5-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.0-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.0-2",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.1-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.2-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.2-1~deb13u1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.3-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.3-1~deb13u1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.4-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.4-2",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.5-1",
"evidence": "/affected/1/versions"
},
{
"value": "2.8.5-2",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "expat",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "2.8.4-1",
"evidence": "/affected/2/ranges"
}
],
"affected_versions": [
{
"value": "2.7.1-2",
"evidence": "/affected/2/versions"
},
{
"value": "2.7.2-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.7.3-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.7.3-2",
"evidence": "/affected/2/versions"
},
{
"value": "2.7.4-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.7.5-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.0-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.0-2",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.1-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.2-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.2-1~deb13u1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.3-1",
"evidence": "/affected/2/versions"
},
{
"value": "2.8.3-1~deb13u1",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "high",
"structured": {
"id": "DEBIAN-CVE-2026-66046",
"aliases": [
"DEBIAN-CVE-2026-66046"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "2.5.0-1+deb12u4"
}
]
}
],
"package": {
"name": "expat",
"purl": "pkg:deb/debian/expat?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"2.5.0-1",
"2.5.0-1+deb12u1",
"2.5.0-1+deb12u2",
"2.5.0-1+deb12u3"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-66046.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "2.9.0-1~deb13u1"
}
]
}
],
"package": {
"name": "expat",
"purl": "pkg:deb/debian/expat?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"2.7.1-2",
"2.7.2-1",
"2.7.3-1",
"2.7.3-2",
"2.7.4-1",
"2.7.5-1",
"2.8.0-1",
"2.8.0-2",
"2.8.1-1",
"2.8.2-1",
"2.8.2-1~deb13u1",
"2.8.3-1",
"2.8.3-1~deb13u1",
"2.8.4-1",
"2.8.4-2",
"2.8.5-1",
"2.8.5-2"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-66046.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "2.8.4-1"
}
]
}
],
"package": {
"name": "expat",
"purl": "pkg:deb/debian/expat?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"2.7.1-2",
"2.7.2-1",
"2.7.3-1",
"2.7.3-2",
"2.7.4-1",
"2.7.5-1",
"2.8.0-1",
"2.8.0-2",
"2.8.1-1",
"2.8.2-1",
"2.8.2-1~deb13u1",
"2.8.3-1",
"2.8.3-1~deb13u1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-66046.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-23T17:47:31.770099504Z",
"provider": "osv",
"upstream": [
"CVE-2026-66046"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-66046"
]
},
"related_cves": [
{
"value": "CVE-2026-66046",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 417446,
"published_at": "2026-08-18T15:16:57+00:00"
}