Description
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.
Published: 2026-08-18
Score: 8.7 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Fri, 21 Aug 2026 12:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 18 Aug 2026 16:15:00 +0000

Type Values Removed Values Added
First Time appeared Libexpat Project
Libexpat Project libexpat
Vendors & Products Libexpat Project
Libexpat Project libexpat

Tue, 18 Aug 2026 14:30:00 +0000

Type Values Removed Values Added
Description 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.
Title Expat Denial of Service via storeAtts() Quadratic Complexity
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 8.7, 'vector': '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'}


Subscriptions

Libexpat Project Libexpat
cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-08-21T11:20:55.742Z

Reserved: 2026-07-23T20:45:17.817Z

Link: CVE-2026-66046

cve-icon Vulnrichment

Updated: 2026-08-20T13:48:25.851Z

cve-icon NVD

Status : Received

Published: 2026-08-18T15:16:57.000

Modified: 2026-08-20T16:17:40.660

Link: CVE-2026-66046

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-18T16:15:04Z

Weaknesses