Detections
Analytics

Amazon Linux 2 : perl (ALAS-2026-4026)

medium Nessus Plugin ID 371767

Synopsis

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

Description

The version of perl installed on the remote host is prior to 5.16.3-299. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-4026 advisory.

 Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch.

 The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes. Nothing checks that product for positive overflow of the signed 32-bit count: a 286331153 byte subject matched against a pattern with 15 participating nodes stores the count as 14, leaving a two byte cache. The cache is then indexed from the real match position and node number, so reads go past the end of the allocation, and on failure CACHEsayNO sets a bit past it.

 A caller that matches an attacker controlled subject of this size against a pattern of this shape can crash the process or corrupt heap memory. (CVE-2026-15534)

 Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass.

 The prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds.

 Example:

 ABCDE =~ m/ABCF|BCDE|C/; # matches C at offset 2, not BCDEABCDE =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed

 An alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong. (CVE-2026-19487)

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 'yum update perl' or or 'yum update --advisory ALAS2-2026-4026' to update your system.

See Also

https://alas.aws.amazon.com//AL2/ALAS2-2026-4026.html

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

https://explore.alas.aws.amazon.com/CVE-2026-15534.html

https://explore.alas.aws.amazon.com/CVE-2026-19487.html

Plugin Details

Severity: Medium

ID: 371767

File Name: al2_ALAS-2026-4026.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 10/24/2026

Updated: 10/24/2026

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: 5.5

Percentile: 95.72

CVSS v2

Risk Factor: Medium

Base Score: 4.7

Temporal Score: 3.5

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

CVSS Score Source: CVE-2026-15534

CVSS v3

Risk Factor: Medium

Base Score: 5.7

Temporal Score: 5

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

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

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:perl-core, p-cpe:/a:amazon:linux:perl-cpan, p-cpe:/a:amazon:linux:perl-debuginfo, p-cpe:/a:amazon:linux:perl-devel, p-cpe:/a:amazon:linux:perl-extutils-cbuilder, p-cpe:/a:amazon:linux:perl-extutils-embed, p-cpe:/a:amazon:linux:perl-extutils-install, p-cpe:/a:amazon:linux:perl-io-zlib, p-cpe:/a:amazon:linux:perl-libs, p-cpe:/a:amazon:linux:perl-locale-maketext-simple, p-cpe:/a:amazon:linux:perl-macros, p-cpe:/a:amazon:linux:perl-module-corelist, p-cpe:/a:amazon:linux:perl-module-loaded, p-cpe:/a:amazon:linux:perl-object-accessor, p-cpe:/a:amazon:linux:perl-package-constants, p-cpe:/a:amazon:linux:perl-pod-escapes, p-cpe:/a:amazon:linux:perl-tests, p-cpe:/a:amazon:linux:perl-time-piece, p-cpe:/a:amazon:linux:perl

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

Exploit Ease: No known exploits are available

Patch Publication Date: 10/24/2026

Vulnerability Publication Date: 8/9/2026

Reference Information

CVE: CVE-2026-15534, CVE-2026-19487

IAVA: 2026-A-0889