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CVE-2026-66046

Expat Denial of Service via storeAtts() Quadratic Complexity

Published: Aug 18, 2026Updated: Aug 20, 2026 Sources: CVE List NVDCWE-407
7.5HIGH
NVD MITRE
EPSS Score
0.6%
Top 54.1%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available
Self-Check
OpenVAS

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
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Weaknesses

CWE-407

Affected Products

libexpat project
oss-projectaka libexpat, expat
libexpatLibraryLibrary
OSS Libraries / generic-library

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.
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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://github.com/libexpat/libexpat/pull/1321
github.com
https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity
vulncheck.com

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