Potential Linux SSH X11 Forwarding

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This rule monitors for X11 forwarding via SSH. X11 forwarding is a feature that allows users to run graphical applications on a remote server and display the application’s graphical user interface on their local machine. Attackers can abuse X11 forwarding for tunneling their GUI-based tools, pivot through compromised systems, and create covert communication channels, enabling lateral movement and facilitating remote control of systems within a network.

Rule type: eql

Rule indices:

  • logs-endpoint.events.*

Severity: low

Risk score: 21

Runs every: 60m

Searches indices from: now-119m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Endpoint
  • OS: Linux
  • Use Case: Threat Detection
  • Tactic: Command and Control
  • Data Source: Elastic Defend
  • Rule Type: BBR

Version: 1

Rule authors:

  • Elastic

Rule license: Elastic License v2

Rule query

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process where host.os.type == "linux" and event.action == "exec" and event.type == "start" and
process.name in ("ssh", "sshd") and process.args in ("-X", "-Y") and process.args_count >= 3 and
process.parent.name in ("bash", "dash", "ash", "sh", "tcsh", "csh", "zsh", "ksh", "fish")

Framework: MITRE ATT&CKTM