CVE-2026-66046 Expat Denial of Service via storeAtts() Quadratic Complexity
Remote attackers can cause denial of service in applications using Expat by submitting large XML documents that trigger quadratic complexity in attribute processing.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-66046?
CVE-2026-66046 is a high-severity denial of service vulnerability in Libexpat Project Libexpat, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-407
Which versions are affected by CVE-2026-66046?
It affects 1 product.
Products include Libexpat Project Libexpat.
How do I fix CVE-2026-66046?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-66046 being exploited?
There is no known exploitation of CVE-2026-66046 in the wild and no public exploit code.
Other vulnerabilities in Libexpat Project Libexpat
Sources
Also known as ALPINE-CVE-2026-66046, AZL-96605, BELL-CVE-2026-66046, CLSA-2026-1790064092, CLSA-2026-1790153508, CLSA-2026-1790239193 and 7 more.