CVE-2026-66046

  1. OpenCVE
  2. Vulnerabilities (CVE)
  3. CVE-2026-66046
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.

7.5 /10

CVSS v3 : HIGH

V3 Legend

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References
Link Resource
https://github.com/libexpat/libexpat/pull/1321 Exploit Patch Vendor Advisory
https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity Exploit Patch Third Party Advisory
Configurations

Configuration 1 (hide)

cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*
History

22 Oct 2026, 22:10

Type Values Removed Values Added
Summary
  • (es) Expat hasta 2.8.3 contiene una vulnerabilidad de denegación de servicio causada por la complejidad algorítmica cuadrática en la función storeAtts() en xmlparse.c, donde el procesamiento de N atributos especificados con valores no normalizados desencadena un escaneo lineal O(N^2) de elementType -> defaultAtts para determinar el estado CDATA. Un atacante remoto no autenticado puede suministrar un único documento XML bien formado de unos pocos megabytes a una aplicación que analiza XML no confiable para causar un consumo excesivo de CPU, lo que resulta en denegación de servicio sin requerir autenticación, resolución de entidades externas u opciones de analizador no predeterminadas.

18 Sep 2026, 15:07

Type Values Removed Values Added
CPE cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*
First Time Libexpat Project
Libexpat Project libexpat
References () https://github.com/libexpat/libexpat/pull/1321 - () https://github.com/libexpat/libexpat/pull/1321 - Exploit, Patch, Vendor Advisory
References () https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity - () https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity - Exploit, Patch, Third Party Advisory
Information

Published : 2026-08-18 15:16

Updated : 2026-10-22 22:10

NVD link : CVE-2026-66046

Mitre link : CVE-2026-66046

CVE.ORG link : CVE-2026-66046

JSON object : View

Products Affected

libexpat_project

  • libexpat
CWE
CWE-407

Inefficient Algorithmic Complexity