IAM

AWS Systems Manager Agent Flaw Allows Bypass of Port Forwarding Restrictions

Amazon has fixed a vulnerability in the AWS Systems Manager agent that permits an authenticated attacker to bypass restrictions on port forwarding sessions. The issue, tracked as CVE-2026-89049, stems from inadequate validation of equivalent representations of blocked link-local addresses. As a result, attackers can reach the EC2 instance metadata service at 169.254.169.254 and obtain temporary credentials tied to the instance's IAM role. Affected versions are those prior to 3.3.4851.0, with the fix included in that release and all subsequent versions. AWS recommends reviewing custom builds of the agent, restricting access to the AWS-StartPortForwardingSessionToRemoteHost document, auditing Session Manager activity, and applying least-privilege principles to IAM roles.