Amazon Linux 2023 Security Advisory: ALAS2023-2026-3160
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
Issue Correction:
Run dnf update amazon-ssm-agent --releasever 2023.12.20261012 or dnf update --advisory ALAS2023-2026-3160 --releasever 2023.12.20261012 to update your system.
More information on how to update your system can be found on this page: Amazon Linux 2023 documentation
aarch64:
amazon-ssm-agent-3.3.5390.0-1.amzn2023.aarch64
src:
amazon-ssm-agent-3.3.5390.0-1.amzn2023.src
x86_64:
amazon-ssm-agent-3.3.5390.0-1.amzn2023.x86_64