Amazon Linux 2 : amazon-ssm-agent, --advisory ALAS2-2026-3809 (ALAS-2026-3809)

high Nessus Plugin ID 328842

Synopsis

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

Description

The version of amazon-ssm-agent installed on the remote host is prior to 3.3.4624.0-1. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3809 advisory.

An authenticated SSH client that repeatedly opened channels which were rejected by the server caused unbounded memory growth, eventually crashing the server process and affecting all connected users.
Rejected channels are now properly removed from the connection's internal state and released for garbage collection. (CVE-2026-39827)

The RSA and DSA public key parsers did not enforce size limits on key parameters. A crafted public key with an excessively large modulus or DSA parameter could cause several minutes of CPU consumption during signature verification. This could be triggered by unauthenticated clients during public key authentication. RSA moduli are now limited to 8192 bits, and DSA parameters are validated per FIPS 186-2.
(CVE-2026-39829)

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded. (CVE-2026-39830)

The Verify() method for FIDO/U2F security key types ([email protected], sk-ssh- [email protected]) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a no-touch-required extension in Permissions.Extensions from PublicKeyCallback. (CVE-2026-39831)

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation. (CVE-2026-39834)

SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or IsHostAuthority could be caused to panic by a client presenting a certificate. CertChecker now returns an error instead of panicking when these callbacks are nil. (CVE-2026-39835)

go-git is an extensible git implementation library written in pure Go. Prior to versions 5.18.0 and 6.0.0-alpha.2, go-git may leak HTTP authentication credentials when following redirects during smart-HTTP clone and fetch operations. This issue has been patched in versions 5.18.0 and 6.0.0-alpha.2.
(CVE-2026-41506)

Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation. Now, both the 'key' and 'key.SignatureKey' are checked for @revoked. (CVE-2026-42508)

An incorrectly placed cast from bytes to int allowed for server-side panic in the AES-GCM packet decoder for well-crafted inputs. (CVE-2026-46597)

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 amazon-ssm-agent' or or 'yum update --advisory ALAS2-2026-3809' to update your system.

Plugin Details

Severity: High

ID: 328842

File Name: al2_ALAS-2026-3809.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 7/21/2026

Updated: 7/21/2026

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: 4.3

Percentile: 53.62

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 5.8

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

CVSS Score Source: CVE-2026-41506

CVSS v3

Risk Factor: High

Base Score: 7.4

Temporal Score: 6.4

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

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

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:amazon-ssm-agent

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

Exploit Ease: No known exploits are available

Patch Publication Date: 7/20/2026

Vulnerability Publication Date: 4/17/2026

Reference Information

CVE: CVE-2026-39827, CVE-2026-39829, CVE-2026-39830, CVE-2026-39831, CVE-2026-39834, CVE-2026-39835, CVE-2026-41506, CVE-2026-42508, CVE-2026-46597

IAVB: 2026-B-0120

Detections

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