Critical SSRF Vulnerability in AWS SSM Agent Allows IAM Credential Theft via Port Forwarding Bypass
Amazon Web Services has published a security advisory detailing a serious vulnerability in the AWS Systems Manager Agent (SSM Agent). The software works in conjunction with the cloud management service AWS Systems Manager to enable remote administration of EC2 instances and on-premises servers.
The flaw, identified as CVE-2026-89049, is a server-side request forgery (SSRF) issue located in the port-forwarding functionality of Session Manager. Insufficient input validation allows an attacker who already possesses port-forwarding rights to bypass deny-list protections by encoding link-local addresses in alternative formats.
Successful exploitation could let an attacker reach link-local endpoints from a managed instance and retrieve temporary security credentials associated with the instance’s IAM role. These credentials could then be used to access other AWS resources within the same account.
AWS assigned the advisory a severity rating of “Important.” The vulnerability received a CVSSv4.0 base score of 8.5 and a CVSSv3.1 base score of 9.9.
The company stated that the issue was resolved in version 3.3.4851.0 of the SSM Agent, released on 13 July 2026. Customers are advised to ensure all managed instances are running the patched agent version.
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