ESXi File Made Executable with chmod

Detects chmod making a file executable on an ESXi host, including +x and numeric modes such as 755 and 777. The host will not run a file until the execute bit is set. Making a file under /tmp executable is the step that lets a later command launch it against the datastore.

Rule type: query
Rule indices:

  • logs-vsphere.log-*

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: now-9m
Maximum alerts per execution: 100
References:

Tags:

  • Domain: Endpoint
  • Data Source: VMware vSphere
  • Use Case: Threat Detection
  • Tactic: Defense Evasion
  • Resources: Investigation Guide
  • Rule Type: Custom Query (KQL)
  • Platform: VMware ESXi
  • Threat: Ransomware

Version: 1
Rule authors:

  • Elastic

Rule license: Elastic License v2

This rule requires ESXi host logs collected by the Elastic vSphere integration: https://www.elastic.co/docs/reference/integrations/vsphere

chmod +x, chmod a+x, and numeric modes such as 777 and 755 add the execute bit. On ESXi this is the step that turns a file dropped in /tmp into a runnable payload. Modes that do not grant execute, such as 644, are not included.

  • Read the full command in message, including the target path.
  • Check the same session for a copy into /tmp, a following execution of that path, VM process kills, or a search for vmdk files.
  • Confirm with the virtualization owner whether that file was part of an approved script.

Support workflows sometimes chmod a known script. A chmod of an unknown file under /tmp, followed by execution, is the staging pattern.

  • If the file was not approved, remove it and end the shell session.
  • Preserve shell.log and review commands issued after the chmod.
  • If the path was executed, isolate the host and rotate credentials used in that session.
data_stream.dataset:vsphere.log and event.module:vsphere and message:(chmod and ("+x" or 0511 or 0555 or 0700 or 0711 or 0750 or 0755 or 0775 or 0777 or 111 or 1777 or 4755 or 511 or 555 or 700 or 711 or 750 or 755 or 775 or 777 or "a+x" or "g+x" or "o+x" or "u+x"))

Framework: MITRE ATT&CK