CVE-2026-66046Expat Denial of Service via storeAtts() Quadratic Complexity
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- CWE-407
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- VulnCheck
- NVD analysis
- Analyzed
- Record last updated
- Oct 1, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
libexpat project libexpat libexpat_project:libexpat (from the name) | through 2.8.3 | CNA record |
libexpat_project libexpat libexpat_project:libexpat | through 2.8.3 | NVD |
References
- https://github.com/libexpat/libexpat/pull/1321issue-tracking, exploit, patch, vendor-advisory
- https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexitythird-party-advisory, exploit, patch
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.