CVE-2026-66046
Expat Denial of Service via storeAtts() Quadratic Complexity
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-407 |
| Vendor | libexpat project |
| Product | libexpat |
| Published | Aug 18, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected Versions
libexpat project / libexpat
0 ≤ 2.8.3
References
Credits
Fabian Wahle (Hap Security) Sebastian Pipping VulnCheck