T1563.001No distinct observable

SSH Hijacking

Lateral MovementLinux, macOS

Where this stands

A reviewer read the telemetry and concluded there is nothing here to detect that a sibling technique does not already cover.

Both analytics define the technique by two things Sigma cannot hold: a cross-UID ownership comparison and the absence of a prior authentication event. AN0710 (Linux) asks for open/connect syscalls on /tmp/ssh-* or $SSH_AUTH_SOCK where the socket is not owned by the accessing process's user — no single field carries that comparison, it is a join between the file's owning uid and the process's uid, and without it the selector degrades to 'something touched an ssh agent socket', which ssh, ssh-add and every terminal in a forwarded-agent session do constantly. […]

Covered instead by T1021.004, T1563.

What the technique is

Adversaries may hijack a legitimate user's SSH session to move laterally within an environment. Secure Shell (SSH) is a standard means of remote access on Linux and macOS systems. It allows a user to connect to another system via an encrypted tunnel, commonly authenticating through a password, certificate or the use of an asymmetric encryption key pair. In order to move laterally from a compromised host, adversaries may take advantage of trust relationships established with other systems via public key authentication in active SSH sessions by hijacking an existing connection to another system. This may occur through compromising the SSH agent itself or by having access to the agent's socket. If an adversary is able to obtain root access, then hijacking SSH sessions is likely trivial. SSH Hijacking differs from use of SSH because it hijacks an existing SSH session rather than creating a new session using Valid Accounts.

Read it on attack.mitre.org

What MITRE says you would watch

AN0710
Suspicious reuse of SSH agent sockets across multiple users or processes, anomalous access to ~/.ssh/ or /tmp/ssh-* sockets, and abnormal patterns of lateral movement via SSH without new authentication events. Defender view: detect when one process accesses another user's SSH agent or when an existing SSH connection is used to pivot unexpectedly.
AN0711
Unusual access to SSH agent sockets in /tmp/ or /private/tmp, process access to another user’s $SSH_AUTH_SOCK, and lateral SSH activity without corresponding login events. Defender view: correlation of socket access with anomalous network flows to internal systems.