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
Risk score: 73
Runs every: 5 minutes
Maximum alerts per execution: 100
- Threat Detection
Added (Elastic Stack release): 8.3.0
Rule authors: Elastic
Rule license: Elastic License v2
False-Positives (FP) should be at a minimum with this detection as PID files are meant to hold process IDs, not inherently be executables that spawn processes.
## Triage and analysis ### Investigating Process Started from Process ID (PID) File 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.
process where event.type == "start" and user.id == "0" and process.executable regex~ """/var/run/\w+\.(pid|lock|reboot)"""