Detect Clear Linux or Mac System Logs in CrowdStrike LogScale
Adversaries clear system logs on Linux and macOS to remove evidence of intrusion. Primary targets include /var/log/auth.log or /var/log/secure (authentication), /var/log/syslog or /var/log/messages (general), /var/log/wtmp and /var/log/btmp (login records), and web server logs (/var/log/apache2/, /var/log/nginx/). Common methods include truncating files (echo > /var/log/auth.log), deletion (rm /var/log/*.log), or overwriting with zeros. TeamTNT (crypto-mining), Rocke, Sea Turtle (DNS hijacking), Salt Typhoon (telecom espionage), UPSTYLE (Volt Typhoon PANW exploit), and MacMa (macOS) have all cleared Linux/macOS logs post-compromise.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1070 Indicator Removal
- Sub-technique
- T1070.002 Clear Linux or Mac System Logs
- Canonical reference
- https://attack.mitre.org/techniques/T1070/002/
LogScale Detection Query
#event_simpleName = /^(FileDeleteInfo|PeFileWritten|EngineFileWritten)$/
| TargetFileName = /\/(var\/log|Library\/Logs|private\/var\/log)\//
| TargetFileName = /(\.log$|auth\.log|syslog|messages|secure|wtmp|btmp|lastlog|kern\.log)/
| CommandLine != /logrotate|newsyslog|rsyslog|syslogd|aslmanager/
| FileName != /logrotate|newsyslog|rsyslog|syslogd/
| select([timestamp, ComputerName, UserName, FileName, TargetFileName, CommandLine, #event_simpleName])
| sort(timestamp, order=desc)CrowdStrike LogScale (Humio) query against Falcon endpoint telemetry detecting FileDeleteInfo and file write events (PeFileWritten/EngineFileWritten used for truncation patterns) on Linux and macOS log paths. Filters on target file path regex matching /var/log/, /Library/Logs/, and known log file names, excluding legitimate log rotation executables.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon sensor self-diagnostics or log cleanup within monitored paths that use non-standard process names not captured in the exclusion filter
- Linux package managers (rpm, dpkg) triggering prerm or postrm scripts that remove log files associated with an uninstalled service package
- macOS Time Machine or third-party backup agents that stage log files before archival, temporarily appearing as deletion events
Other platforms for T1070.002
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 1Clear Linux Auth Log via Truncation
Expected signal: auditd: SYSCALL records showing open with O_TRUNC flag on /var/log/auth.log. File modification event captured by endpoint telemetry. rsyslog may log a restart after the file is truncated if it monitors file size.
- Test 2Delete /var/log Files Using rm
Expected signal: auditd: SYSCALL records for creat/open (file creation) and unlink (file deletion). File creation and deletion events in endpoint telemetry. The file creation followed immediately by deletion pattern is anomalous.
- Test 3Clear Login History via wtmp Manipulation
Expected signal: auditd: SYSCALL for open with O_TRUNC on /var/log/wtmp. Any process monitoring wtmp (e.g., login daemons) may detect the size change. File modification event in endpoint telemetry for wtmp.
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