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CVE-2026-66046 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/libexpat/libexpat/pull/1321	[email protected]	ExploitPatchVendor Advisory
https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity	[email protected]	ExploitPatchThird Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-407	Inefficient Algorithmic Complexity	[email protected]

Affected Products

Product	Versions
libexpat project libexpat	<= 2.8.3
CPE cpe:2.3:a:libexpat_project:libexpat:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Sep 18, 2026	Initial Analysis	[email protected]
Aug 20, 2026	CVE Modified	CISA-ADP
Aug 18, 2026	New CVE Received	[email protected]