Remote Service Session Hijacking: SSH Hijacking

ID Name
T1563.001 SSH Hijacking
T1563.002 RDP 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.[1][2][3][4]

SSH Hijacking differs from use of SSH because it hijacks an existing SSH session rather than creating a new session using Valid Accounts.

ID: T1563.001
Sub-technique of:  T1563
Tactic: Lateral Movement
Platforms: Linux, macOS
System Requirements: SSH service enabled, trust relationships configured, established connections
Permissions Required: root
Data Sources: Authentication logs
Contributors: Anastasios Pingios
Version: 1.0
Created: 25 February 2020
Last Modified: 23 March 2020

Mitigations

Mitigation Description
Disable or Remove Feature or Program

Ensure that agent forwarding is disabled on systems that do not explicitly require this feature to prevent misuse. [5]

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.

Privileged Account Management

Do not allow remote access via SSH as root or other privileged accounts.

Restrict File and Directory Permissions

Ensure proper file permissions are set and harden system to prevent root privilege escalation opportunities.

Detection

Use of SSH may be legitimate, depending upon the network environment and how it is used. Other factors, such as access patterns and activity that occurs after a remote login, may indicate suspicious or malicious behavior with SSH. 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.

References