Amazon Linux 2023 : expat, expat-devel, expat-static (ALAS2023-2026-2157)

high Nessus Plugin ID 345784

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Synopsis

The remote Amazon Linux 2023 host is missing a security update.

Description

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-2157 advisory.

libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse, XML_ParseBuffer, XML_ParserFree, or XML_ParserReset from within handlers in cases of a policy violation.
Thus, a use-after-free can occur, (CVE-2026-50219)

libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in cases of a policy violation. Thus, a use-after-free can occur (similar to the CVE-2026-50219 situation). (CVE-2026-56131)

libexpat before 2.8.2 has an integer overflow in addBinding. (CVE-2026-56404)

libexpat before 2.8.2 has an integer overflow in getAttributeId. (CVE-2026-56405)

libexpat before 2.8.2 has an integer overflow in copyString. (CVE-2026-56408)

xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputDir is used.
(CVE-2026-56409)

xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId. (CVE-2026-56410)

xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarations.
(CVE-2026-56411)

libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls from within handlers in cases of a policy violation. Thus, a use-after- free can occur. NOTE: this issue exists because of an incomplete fix for CVE-2026-50219. (CVE-2026-56412)

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)

libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after- free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.
(CVE-2026-76957)

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

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

Solution

Run 'dnf update expat --releasever 2023.12.20260914' or or 'dnf update --advisory ALAS2023-2026-2157 --releasever 2023.12.20260914' to update your system.

Plugin Details

Severity: High

ID: 345784

File Name: al2023_ALAS2023-2026-2157.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 9/14/2026

Updated: 9/14/2026

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: Medium

Score: 4.9

Percentile: 58.15

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

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

CVSS Score Source: CVE-2026-76957

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

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

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

CVSS v4

Risk Factor: High

Base Score: 8.7

Threat Score: 6.6

Threat Vector: CVSS:4.0/E:U

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

CVSS Score Source: CVE-2026-66046

Vulnerability Information

CPE: cpe:/o:amazon:linux:2023, p-cpe:/a:amazon:linux:expat-debuginfo, p-cpe:/a:amazon:linux:expat-debugsource, 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 Ease: No known exploits are available

Patch Publication Date: 9/14/2026

Vulnerability Publication Date: 6/4/2026

Reference Information

CVE: CVE-2026-50219, CVE-2026-56131, CVE-2026-56404, CVE-2026-56405, CVE-2026-56408, CVE-2026-56409, CVE-2026-56410, CVE-2026-56411, CVE-2026-56412, CVE-2026-66046, CVE-2026-76957

IAVA: 2026-A-0650-S, 2026-A-0925

Detections

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