Amazon Linux 2 : amazon-cloudwatch-agent (ALAS-2026-4049)

critical Nessus Plugin ID 374388

Synopsis

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

Description

The version of amazon-cloudwatch-agent installed on the remote host is prior to 1.300073.2-1. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-4049 advisory.

Due to security concerns regarding a small set of intermediate certificates issued by a specific Certificate Authority (CA), the Go's crypto/x509 package is updated to not trust certificates issued by the affected intermediate certificates. This would prevent possible future misuse of certificate issued by the affected intermediate certificates.

Amazon Linux golang-based packages are being rebuilt with the fixed crypto/x509 package described in CVE-2026-111943 as a defense-in-depth measure against the eMudhra intermediate CA certificates with weak private keys.

By default, Go programs on Amazon Linux use the system-wide certificate authority (CA) store. Therefore, the primary fix for this issue is the ca-certificates update that removes the root CA certificates that signed the affected intermediates. Customers should ensure that update is installed:
https://explore.alas.aws.amazon.com/CVE-2026-113470.html (CVE-2026-111943)

When Trailer headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a Trailer header that declares a large number of fields causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits.This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits are now applied towards the trailer fields declared in Trailer headers.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9NOTE:
https://github.com/golang/go/issues/81857NOTE: Fixed by:
https://github.com/golang/go/commit/cbb0fb8b51cba866018b8a0fb4b5458f16c5c80b (go1.27.2)NOTE: Fixed by:
https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-78659)

The HTTP/2 server could refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data.A malicious client could exploit this to bypass the configured connection- level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control.The HTTP/2 server now waits to refund connection- level flow control for reset streams until after the request handler is complete.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9NOTE:
https://github.com/golang/go/issues/81743NOTE: Fixed by:
https://github.com/golang/go/commit/31dc9e2449e394439498142451627af52626d7c4 (go1.27.2)NOTE: Fixed by:
https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-78663)

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-cloudwatch-agent' or or 'yum update --advisory ALAS2-2026-4049' to update your system.

Plugin Details

Severity: Critical

ID: 374388

File Name: al2_ALAS-2026-4049.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 10/30/2026

Updated: 10/30/2026

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: High

Score: 7.3

Percentile: 98.16

CVSS v2

Risk Factor: High

Base Score: 9.4

Temporal Score: 7

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

CVSS Score Source: CVE-2026-78663

CVSS v3

Risk Factor: Critical

Base Score: 9.1

Temporal Score: 7.9

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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:amazon-cloudwatch-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: 10/30/2026

Vulnerability Publication Date: 10/8/2026

Reference Information

CVE: CVE-2026-111943, CVE-2026-78659, CVE-2026-78663

IAVB: 2026-B-0296-S, 2026-B-0304

Detections

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