Detect Remote Service Session Hijacking in Microsoft Sentinel
This detection identifies adversaries commandeering existing remote service sessions to move laterally without creating new authenticated connections. Key indicators include use of tscon.exe to hijack disconnected RDP sessions (often from SYSTEM context), SSH agent socket manipulation via SSH_AUTH_SOCK environment variable abuse, SSH ControlMaster/ControlPath multiplexing attacks, and suspicious processes accessing other users' TTY devices or SSH agent sockets in /tmp. Unlike standard remote service use, session hijacking leaves minimal authentication artifacts because no new credential exchange occurs — making it a high-fidelity signal when detected.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1563 Remote Service Session Hijacking
- Canonical reference
- https://attack.mitre.org/techniques/T1563/
KQL Detection Query
let RDPHijack = DeviceProcessEvents
| where FileName =~ "tscon.exe"
or (FileName in~ ("cmd.exe", "powershell.exe") and ProcessCommandLine has "tscon")
| extend HijackType = "RDP_tscon"
| extend RiskDetail = strcat("tscon invoked by: ", InitiatingProcessFileName, " as ", AccountName);
let SSHAgentHijack = DeviceProcessEvents
| where ProcessCommandLine has_any ("SSH_AUTH_SOCK", "/tmp/ssh-", "ssh-agent")
and ProcessCommandLine has_any ("export", "env", "printenv", "cat /proc")
and not (FileName in~ ("sshd", "ssh-agent"))
| extend HijackType = "SSH_Agent_Hijack"
| extend RiskDetail = strcat("SSH_AUTH_SOCK access by non-ssh process: ", FileName);
let SSHControlMaster = DeviceProcessEvents
| where FileName =~ "ssh"
and ProcessCommandLine has_any ("ControlMaster", "ControlPath", "-o ControlMaster", "-S /tmp")
and not (InitiatingProcessFileName in~ ("sshd", "ansible", "fabric"))
| extend HijackType = "SSH_ControlMaster_Abuse"
| extend RiskDetail = strcat("SSH multiplexing hijack attempt from: ", InitiatingProcessFileName);
let TTYHijack = DeviceProcessEvents
| where ProcessCommandLine has_any ("/proc/", "/dev/pts/", "reptyr", "injcode")
and ProcessCommandLine matches regex @"/proc/\d+/fd"
| extend HijackType = "TTY_Hijack"
| extend RiskDetail = "Process fd hijack targeting remote session TTY";
union RDPHijack, SSHAgentHijack, SSHControlMaster, TTYHijack
| project
TimeGenerated,
DeviceName,
AccountName,
HijackType,
RiskDetail,
FileName,
ProcessCommandLine,
InitiatingProcessFileName,
InitiatingProcessCommandLine,
InitiatingProcessAccountName,
FolderPath
| order by TimeGenerated descDetects four patterns of remote service session hijacking: (1) tscon.exe used to redirect RDP sessions, often from SYSTEM context to hijack disconnected sessions without credentials; (2) non-SSH processes accessing SSH_AUTH_SOCK for agent forwarding abuse; (3) SSH ControlMaster/ControlPath multiplexing abuse to piggyback on existing authenticated connections; (4) /proc/pid/fd TTY descriptor hijacking targeting active terminal sessions.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate IT administrators using tscon.exe for authorized session management or helpdesk reconnection workflows
- Ansible, Fabric, or other automation tools that legitimately use SSH ControlMaster for connection multiplexing to improve performance
- SSH agent forwarding used by developers or DevOps engineers for legitimate key forwarding across jump hosts
Other platforms for T1563
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1RDP Session Hijacking via tscon.exe from SYSTEM context
Expected signal: Sysmon Event ID 1 for tscon.exe with parent process chain including psexec/sc.exe. Windows Security Event 4778 (session reconnected) immediately after. Security Event 4688 for tscon.exe with SYSTEM account. Query.exe or qwinsta.exe execution preceding tscon.exe within minutes.
- Test 2SSH Agent Socket Hijacking
Expected signal: Auditd records showing open() syscall on /tmp/ssh-*/agent.* socket by a process not owned by the socket's owner. /var/log/auth.log entries showing SSH connection authenticated via agent forwarding with unexpected source process context. Linux Sysmon (if deployed) Event ID 1 for ssh process with SSH_AUTH_SOCK in environment.
- Test 3SSH ControlMaster Multiplexing Session Hijack
Expected signal: Sysmon (Linux) Event ID 1 for ssh process with -S flag and ControlMaster=no in command line. Process events showing ssh invoked with control socket path. Auth.log showing multiple SSH authentications to same host with same session multiplexed. Network events showing SSH connections reusing existing TCP connection.
References (7)
- https://attack.mitre.org/techniques/T1563/
- https://attack.mitre.org/techniques/T1563/001/
- https://attack.mitre.org/techniques/T1563/002/
- https://medium.com/@networksecurity/rdp-hijacking-how-to-hijack-rds-and-remote-mstsc-sessions-transparently-2d941099b086
- https://doublepulsar.com/rdp-hijacking-how-to-hijack-rds-and-remote-mstsc-sessions-transparently-2d941099b086
- https://www.netspi.com/blog/technical/network-penetration-testing/hijacking-ssh-sessions-with-screen-and-command-injection/
- https://xorl.wordpress.com/2022/02/09/ssh-session-hijacking/
Unlock Pro Content
Get the full detection package for T1563 including response playbook, investigation guide, and atomic red team tests.