CVE-2026-66046

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.7% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-18 15:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-22 22:10 UTC Last updatedMost recent change to the record

Details

Published

2026-08-18 15:16 UTC

Last modified

2026-10-22 22:10 UTC

Exploit probability

0.7% · EPSS, next 30 days

Weakness

CWE-407

Record status

Analyzed

Affected

• Libexpat Project Libexpat ≤ 2.8.3

Attack profile CVSS 4.0 · 8.7

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High