A high-severity path traversal vulnerability in the Amazon SSM Agent enables authenticated attackers to achieve arbitrary file writes and root-level code execution.

The vulnerability is a relative path traversal (CWE-23) within the aws:downloadContent plugin. It allows an authenticated remote user, even one with restricted ssm:SendCommand permissions, to escape the intended directory and overwrite sensitive system files using crafted object keys from an S3 source.

The ability to write arbitrary files as root grants an attacker full control over the affected system. Successful exploitation leads to total system compromise, including the potential for data exfiltration, persistent backdoors, and total loss of system integrity. With a CVSS score of 8.8, this flaw represents a significant risk to operational security and server availability.

Immediate Action: Upgrade the amazon-ssm-agent to version 3.3.4515.0 or later immediately to resolve the path validation flaw.

Proactive Monitoring: Monitor AWS CloudTrail logs for unusual ssm:SendCommand activity or unexpected file write operations performed by the SSM agent service account.

Compensating Controls: Restrict IAM policies to ensure only highly trusted identities can trigger the AWS-DownloadContent document, limiting the surface area for potential exploitation.

Public Exploit Available: No

Given the severity of this vulnerability and the potential for root-level code execution, organizations should prioritize the deployment of version 3.3.4515.0 across all managed instances. Security teams should audit current IAM policies to ensure the principle of least privilege is applied to all users with document execution permissions, further reducing the risk of unauthorized command execution while the update is staged.