OpenSSH 10.5 was released on 11 August 2026 with three security fixes. Ubuntu backported them on 3 September 2026 as USN-8721-1, which is when most Ubuntu developer machines and jump hosts could install them. The headline bug, CVE-2026-73281, affects anyone who forwards an ssh-agent to a machine they do not fully control.
What's affected
OpenSSH before 10.5. Ubuntu fixed versions: 22.04 LTS 1:8.9p1-3ubuntu0.17, 24.04 LTS 1:9.6p1-3ubuntu13.19, 26.04 LTS 1:10.2p1-2ubuntu3.6.
- CVE-2026-73281: an interaction between agent locking and the
session-bind@openssh.comextension. A remote attacker with access to a forwarded agent connection could do operations meant to be local only, such as adding tokens or using keys. - CVE-2026-73282: a use-after-free in the ssh client when a remote forwarding is added through session multiplexing while another is pending. Ubuntu says it could lead to denial of service or code execution.
- CVE-2026-73283: the
restrictkeyword inauthorized_keysdid not apply to tunnel forwarding. Tunnel forwarding is off by default.
Later, OpenSSH 10.6 on 6 October added more fixes. Ubuntu bundled those in USN-8928-1 on 14 October.
What to do now
- Update:
sudo apt update && sudo apt install --only-upgrade openssh-client openssh-server, and check withssh -V. - Find who forwards agents:
grep -rn "ForwardAgent" ~/.ssh/config /etc/ssh/ssh_config*. Replace it withProxyJumpwhere you only need to reach a second host. - If you must forward, use
ssh-add -cso each key use asks for confirmation, and restrict keys with destination constraints on OpenSSH versions that support them. - Audit
authorized_keysentries that rely onrestrictto block tunnels, and re-test them after the update.
Quick check
Why is agent forwarding riskier than ProxyJump?
A forwarded agent socket on a remote host can be used by anyone with access to that host as you. ProxyJump keeps the agent on your machine.
