Detections
Analytics

Amazon Linux 2 : expat (ALAS-2026-3965)

high Nessus Plugin ID 365267

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Synopsis

The remote Amazon Linux 2 host is missing a security update.

Description

The version of expat installed on the remote host is prior to 2.1.0-15. It is, therefore, affected by a vulnerability as referenced in the ALAS2-2026-3965 advisory.

 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. (CVE-2026-66046)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Run 'yum update expat' or or 'yum update --advisory ALAS2-2026-3965' to update your system.

See Also

https://alas.aws.amazon.com//AL2/ALAS2-2026-3965.html

https://alas.aws.amazon.com/faqs.html

https://explore.alas.aws.amazon.com/CVE-2026-66046.html

Plugin Details

Severity: High

ID: 365267

File Name: al2_ALAS-2026-3965.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 10/12/2026

Updated: 10/12/2026

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.62

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.1

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:C

CVSS Score Source: CVE-2026-66046

CVSS v3

Risk Factor: High

Base Score: 7.5

Temporal Score: 6.7

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

CVSS v4

Risk Factor: High

Base Score: 8.7

Threat Score: 7.7

Threat Vector: CVSS:4.0/E:P

Vector: 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

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:expat-debuginfo, p-cpe:/a:amazon:linux:expat-devel, p-cpe:/a:amazon:linux:expat-static, p-cpe:/a:amazon:linux:expat

Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 10/12/2026

Vulnerability Publication Date: 8/18/2026

Reference Information

CVE: CVE-2026-66046

IAVA: 2026-A-0925-S