CVE-2026-89049

This is a flaw in a tool used to connect to and manage company servers. It is like a receptionist checking only one spelling of a restricted room's name: someone with building access can use a different spelling to get the receptionist to send them there anyway, potentially reaching protected internal information.

This matters to you if you run Amazon SSM Agent on managed servers and allow people or systems to use its port-forwarding capability. An attacker must already have an authenticated remote account with access to that interface; no extra user action is needed.

Treat this as urgent because a logged-in attacker can use the flaw over the network to reach protected internal endpoints and potentially obtain server cloud credentials. There is no confirmed public exploitation or public exploit code at this time, but the potential access and impact warrant prompt remediation.

Confirm the installed Amazon SSM Agent version on all managed instances and identify principals permitted to use Session Manager port forwarding, especially forwarding to remote hosts. Upgrade every platform to Amazon SSM Agent 3.3.4851.0 or later; the provided findings identify this as the fixed release and do not describe branch-specific alternatives or breaking changes. If patching is delayed, temporarily remove or tightly limit port-forwarding permissions to essential administrators and investigate port-forwarding activity for crafted destination hosts or attempts to access link-local endpoints. CISA has not added this CVE to the Known Exploited Vulnerabilities catalog, so there is no CISA remediation due date. Monitor upgrade completion, Session Manager port-forwarding use, and unusual access involving instance credentials or link-local destinations.

CVE-2026-89049 is rated CVSS 9.9 Critical (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H). It is an authenticated network SSRF issue (CWE-918, CWE-1289) caused by improper validation of equivalent IP-address representations in the Session Manager port-forwarding-to-remote-hosts function. A crafted alternate form of a denied link-local address can bypass the remote-destination denylist, enabling access to internal endpoints and potentially temporary IAM role credentials. CISA KEV does not list this CVE; no clear dated in-the-wild exploitation claim or public exploit code is recorded. EPSS is 0.4% at the 30th percentile with a flat trend.