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Process Started from Process ID (PID) File

Elastic Stack Serverless Security

Identifies a new process starting from a process ID (PID), lock or reboot file within the temporary file storage paradigm (tmpfs) directory /var/run directory. On Linux, the PID files typically hold the process ID to track previous copies running and manage other tasks. Certain Linux malware use the /var/run directory for holding data, executables and other tasks, disguising itself or these files as legitimate PID files.

Rule type: eql

Rule indices:

  • logs-endpoint.events.*

Severity: high

Risk score: 73

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Host
  • Linux
  • Threat Detection
  • Execution
  • BPFDoor

Version: 1

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

Detection alerts from this rule indicate a process spawned from an executable masqueraded as a legitimate PID file which is very unusual and should not occur. Here are some possible avenues of investigation:

  • Examine parent and child process relationships of the new process to determine if other processes are running.
  • Examine the /var/run directory using Osquery to determine other potential PID files with unsually large file sizes, indicative of it being an executable: "SELECT f.size, f.uid, f.type, f.path from file f WHERE path like '/var/run/%%';"
  • Examine the reputation of the SHA256 hash from the PID file in a database like VirusTotal to identify additional pivots and artifacts for investigation.

Rule query

process where event.type == "start" and user.id == "0" and process.executable regex~ """/var/run/\w+\.(pid|lock|reboot)"""

Framework: MITRE ATT&CKTM