CVE-2026-66046

EUVD-2026-60821

18.08.2026, 15:16

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.

Provider	Type	Base Score	Atk. Vector	Atk. Complexity	Priv. Required	Vector
NIST	Primary	7.5 HIGH	NETWORK	LOW	NONE	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Base Score

CVSS 3.x

EPSS Score

Percentile: 53.04%

Affected Products (NVD)

Vendor	Product	Version
libexpat_project	libexpat	𝑥 ≤ 2.8.3

𝑥

= Vulnerable software versions

Debian Releases

Debian Product

Codename

expat

bookworm	vulnerable
bookworm (security)	2.5.0-1+deb12u4 fixed
forky	2.8.4-2 fixed
sid	2.8.5-2 fixed
trixie	no-dsa
trixie (security)	vulnerable

Ubuntu Releases

Ubuntu Product

Codename

expat

bionic	Fixed 2.2.5-3ubuntu0.9+esm5 released
focal	Fixed 2.2.9-1ubuntu0.8+esm3 released
jammy	Fixed 2.4.7-1ubuntu0.9 released
noble	Fixed 2.6.1-2ubuntu0.6 released
resolute	Fixed 2.7.4-1ubuntu0.2 released
trusty	Fixed 2.1.0-4ubuntu1.4+esm13 released
xenial	Fixed 2.1.0-7ubuntu0.16.04.5+esm14 released

apache2

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
trusty	not-affected
xenial	not-affected

apr-util

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
trusty	not-affected
xenial	not-affected

cmake

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
xenial	not-affected

ghostscript

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
xenial	not-affected

texlive-bin

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
xenial	not-affected

xmlrpc-c

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	needs-triage
trusty	needs-triage
xenial	needs-triage

vnc4

bionic	needs-triage
jammy	dne
noble	dne
resolute	dne
trusty	needs-triage
xenial	needs-triage

wbxml2

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	needs-triage
xenial	needs-triage

swish-e

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	needs-triage
xenial	needs-triage

insighttoolkit4

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	dne
resolute	dne
xenial	needs-triage

cadaver

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	needs-triage
xenial	needs-triage

gdcm

bionic	not-affected
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
trusty	not-affected
xenial	not-affected

ayttm

jammy	dne
noble	dne
resolute	dne
xenial	needs-triage

cableswig

jammy	dne
noble	dne
resolute	dne
xenial	needs-triage

coin3

bionic	needs-triage
focal	not-affected
jammy	not-affected
noble	not-affected
resolute	not-affected
trusty	needs-triage
xenial	needs-triage

matanza

bionic	needs-triage
focal	ignored
jammy	ignored
noble	ignored
resolute	ignored
xenial	needs-triage

tdom

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	needs-triage
xenial	needs-triage

vtk

jammy	dne
noble	dne
resolute	dne
trusty	needs-triage
xenial	needs-triage

smart

bionic	needs-triage
jammy	dne
noble	dne
resolute	dne
xenial	needs-triage

firefox

jammy	not-affected
noble	not-affected
resolute	not-affected

thunderbird

jammy	not-affected
noble	not-affected
resolute	not-affected

libxmltok

bionic	needs-triage
focal	needs-triage
jammy	needs-triage
noble	needs-triage
resolute	dne
xenial	needs-triage

Red Hat Enterprise Linux Releases

Red Hat Product

Release

expat

RHEL 8	0:2.5.0-4.el8_10 fixed
RHEL 9	0:2.5.0-6.el9_8.5 fixed

expat-devel

RHEL 8	0:2.5.0-4.el8_10 fixed
RHEL 9	0:2.5.0-6.el9_8.5 fixed

Amazon Linux Releases

Amazon Package

Release

expat

Amazon Linux 2023

0:2.8.3-1.amzn2023.0.1

fixed

expat-debuginfo

Amazon Linux 2023

0:2.8.3-1.amzn2023.0.1

fixed

expat-debugsource

Amazon Linux 2023

0:2.8.3-1.amzn2023.0.1

fixed

expat-devel

Amazon Linux 2023

0:2.8.3-1.amzn2023.0.1

fixed

expat-static

Amazon Linux 2023

0:2.8.3-1.amzn2023.0.1

fixed

firefox

Amazon Linux 2023

0:140.14.0-1.amzn2023.0.1

fixed

firefox-debuginfo

Amazon Linux 2023

0:140.14.0-1.amzn2023.0.1

fixed

firefox-debugsource

Amazon Linux 2023

0:140.14.0-1.amzn2023.0.1

fixed

thunderbird

Amazon Linux 2

0:140.14.0-1.amzn2.0.1

fixed

Azure Linux Releases

Azure Package

Release

expat

Azure Linux 3.0

0:2.8.3-2.azl3

fixed

Known Exploits!

Common Weakness Enumeration

CWE-407 - Inefficient Algorithmic Complexity
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

Vulnerability Media Exposure

[GERMAN] expat: Schwachstelle ermöglicht Denial of Service
Ein Angreifer kann eine Schwachstelle in expat ausnutzen, um einen Denial of Service Angriff durchzuführen.
Published: 2026-08-18T22:00:00+00:00

References

https://github.com/libexpat/libexpat/pull/1321

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