Inefficient Algorithmic Complexity in expat - CVE-2026-66046

Vulnerability identifier: #VU149946

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-66046

CWE-ID: CWE-407

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to algorithmic complexity in attribute declaration handling when parsing XML documents with numerous attributes. A remote attacker can submit a crafted XML document to cause a denial of service.

expat
Ubuntu
openEuler
expat-help
expat-devel
expat-debugsource
expat-debuginfo
expat
expat (Ubuntu package)

Install security update from vendor's website.

expat - update to 2.8.4
expat-help - addressed in versions 2.2.9-33, 2.4.1-31, 2.5.0-27, 2.8.1-8
expat-devel - addressed in versions 2.2.9-33, 2.4.1-31, 2.5.0-27, 2.8.1-8
expat-debugsource - addressed in versions 2.2.9-33, 2.4.1-31, 2.5.0-27, 2.8.1-8
expat-debuginfo - addressed in versions 2.2.9-33, 2.4.1-31, 2.5.0-27, 2.8.1-8
expat - addressed in versions 2.2.9-33, 2.4.1-31, 2.5.0-27, 2.8.1-8
expat (Ubuntu package) - addressed in versions 2.1.0-4ubuntu1.4+esm13, 2.1.0-7ubuntu0.16.04.5+esm14, 2.2.5-3ubuntu0.9+esm5, 2.2.9-1ubuntu0.8+esm3, 2.4.7-1ubuntu0.9, 2.6.1-2ubuntu0.6, 2.7.4-1ubuntu0.2

• https://blog.hartwork.org/posts/expat-2-8-4-released/
• https://github.com/libexpat/libexpat/pull/1321

• Multiple vulnerabilities in libexpat
• openEuler 24.03 LTS SP3 update for expat
• openEuler 24.03 LTS SP1 update for expat
• openEuler 22.03 LTS SP4 update for expat
• openEuler 20.03 LTS SP4 update for expat
• openEuler 24.03 LTS SP4 update for expat
• Ubuntu update for expat