CVE-2026-89049 – Amazon SSM Agent
“One alternate spelling of a blocked address turns a managed instance's own cloud identity into an attacker's passport.”
Amazon has released Amazon SSM Agent version 3.3.4851.0 to fix a critical server-side request forgery flaw in the agent's port forwarding to remote hosts. CVE-2026-89049 has a CVSS score of 9.9, Critical severity. The agent does not properly validate equivalent address representations. An authenticated remote user can write a denied link-local address in an alternate form, slip past the remote destination denylist, and reach link-local endpoints.
The business impact is direct. A successful attack can expose the temporary IAM role credentials of a managed instance. The attacker can then act with that role's permissions from outside the instance and reach any cloud resource the role can access. The flaw affects all platforms running versions earlier than 3.3.4851.0. Upgrade every managed instance to version 3.3.4851.0 or later.
Key Details
- Attack Vector
- Network
- Attack Complexity
- Low
- Privileges Required
- Low
- User Interaction
- None
- CWE Classification
- CWE-918