Amazon Linux 2 (EOS) Security Advisory: ALAS2-2026-3969
Advisory Released Date: 2026-10-12
Advisory Updated Date: 2026-10-12
Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking. (CVE-2026-56855)
Previously, a channel registered in the mux's chanList is not usable until it is established. A malicious peer was able flood the channel's incomingRequests, deadlocking the entire connection. Now, we add an atomic established state, set when a channel becomes usable. Until such a time, handlePacket drops every packet other than the open confirmation/failure, without blocking and without tearing down the connection. (CVE-2026-78662)
Affected Packages:
amazon-ssm-agent
Note:
This advisory is applicable to Amazon Linux 2 (AL2) Core repository. Visit this FAQ section for the difference between AL2 Core and AL2 Extras advisories.
Issue Correction:
Run yum update amazon-ssm-agent or yum update --advisory ALAS2-2026-3969 to update your system.
aarch64:
amazon-ssm-agent-3.3.5390.0-1.amzn2.aarch64
src:
amazon-ssm-agent-3.3.5390.0-1.amzn2.src
x86_64:
amazon-ssm-agent-3.3.5390.0-1.amzn2.x86_64