T1563.001: SSH Hijacking

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.

Positive Technologies products that cover the technique

MaxPatrol SIEM knowledge base

Monitoring of process-start events where command line input contains: — 'grep SSH_AUTH_SOCK /proc/environ' or any other occurrences of the SSH_AUTH_SOCK environment variable; — 'SSH_AUTH_SOCK= ssh @' or 'SSH_AUTH_SOCK= ssh-add –l'.

Expert Required. The technique is detected only with the combination of «PT Product + Expert»

Detection

ID	DS0009	Data source and component	Process: Process Creation	Description	Monitor newly executed processes that may hijack a legitimate user's SSH session to move laterally within an environment.

ID	DS0029	Data source and component	Network Traffic: Network Traffic Content	Description	Monitor and analyze traffic patterns and packet inspection associated to protocol(s) that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).

ID	DS0017	Data source and component	Command: Command Execution	Description	Monitor executed commands and arguments that may hijack a legitimate user's SSH session to move laterally within an environment.

ID	DS0028	Data source and component	Logon Session: Logon Session Creation	Description	Monitor for user accounts logged into systems they would not normally access or access patterns to multiple systems over a relatively short period of time. Also monitor user SSH-agent socket files being used by different users.

ID	DS0029	Data source and component	Network Traffic: Network Traffic Flow	Description	Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious.

ID	Data source and component	Description
DS0009	Process: Process Creation	Monitor newly executed processes that may hijack a legitimate user's SSH session to move laterally within an environment.
DS0029	Network Traffic: Network Traffic Content	Monitor and analyze traffic patterns and packet inspection associated to protocol(s) that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).
DS0017	Command: Command Execution	Monitor executed commands and arguments that may hijack a legitimate user's SSH session to move laterally within an environment.
DS0028	Logon Session: Logon Session Creation	Monitor for user accounts logged into systems they would not normally access or access patterns to multiple systems over a relatively short period of time. Also monitor user SSH-agent socket files being used by different users.
DS0029	Network Traffic: Network Traffic Flow	Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious.

Mitigation

ID	M1022	Name	Restrict File and Directory Permissions	Description	Ensure proper file permissions are set and harden system to prevent root privilege escalation opportunities.

ID	M1042	Name	Disable or Remove Feature or Program	Description	Ensure that agent forwarding is disabled on systems that do not explicitly require this feature to prevent misuse.

ID	M1027	Name	Password Policies	Description	Ensure SSH key pairs have strong passwords and refrain from using key-store technologies such as ssh-agent unless they are properly protected.

ID	M1026	Name	Privileged Account Management	Description	Do not allow remote access via SSH as root or other privileged accounts.

ID	Name	Description
M1022	Restrict File and Directory Permissions	Ensure proper file permissions are set and harden system to prevent root privilege escalation opportunities.
M1042	Disable or Remove Feature or Program	Ensure that agent forwarding is disabled on systems that do not explicitly require this feature to prevent misuse.
M1027	Password Policies	Ensure SSH key pairs have strong passwords and refrain from using key-store technologies such as ssh-agent unless they are properly protected.
M1026	Privileged Account Management	Do not allow remote access via SSH as root or other privileged accounts.