libexpat project up to 2.8.3 Parser xmlparse.c storeAtts N response discrepancy

Summaryinfo

A vulnerability classified as problematic was found in libexpat project libexpat up to 2.8.3. This impacts the function storeAtts of the file xmlparse.c of the component Parser. Such manipulation of the argument N leads to response discrepancy. This vulnerability is traded as CVE-2026-66046. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in libexpat project libexpat up to 2.8.3. Affected by this issue is the function storeAtts of the file xmlparse.c of the component Parser. The manipulation of the argument N with an unknown input leads to a response discrepancy vulnerability. Using CWE to declare the problem leads to CWE-204. The product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere. Impacted is confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-66046 since 07/23/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/18/2026). The MITRE ATT&CK project declares the attack technique as T1592.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Project Management Software

Vendor

• libexpat project

Name

• libexpat

Version

• 2.8.0
• 2.8.1
• 2.8.2
• 2.8.3

CPE 2.3info

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CPE 2.2info

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