Detect Break Process Trees in CrowdStrike LogScale
An adversary may attempt to evade process tree-based analysis by modifying executed malware's parent process ID (PPID). If endpoint protection software leverages the parent-child relationship for detection, breaking this relationship could result in the adversary's behavior not being associated with previous process tree activity. On Linux systems, adversaries may execute a series of Native API calls to alter malware's process tree. For example, adversaries can execute their payload without any arguments, call the fork() API call twice, then have the parent process exit. This creates a grandchild process with no parent process that is immediately adopted by the init system process (PID 1), which successfully disconnects the execution of the adversary's payload from its previous process tree. Another example is using the daemon syscall to detach from the current parent process and run in the background.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1036 Masquerading
- Sub-technique
- T1036.009 Break Process Trees
- Canonical reference
- https://attack.mitre.org/techniques/T1036/009/
LogScale Detection Query
#event_simpleName=ProcessRollup2
| ParentBaseFileName = /^(bash|sh|dash|zsh|ksh|python3?|perl5?|ruby|php|node|lua)$/i
| groupBy(
[ComputerName, UserName, TargetProcessId, FileName, CommandLine, ParentBaseFileName],
function=[
count(as=SpawnCount),
min(ContextTimeStamp, as=FirstSeen),
max(ContextTimeStamp, as=LastSeen),
collect(ParentProcessId, as=ObservedParentPIDs)
]
)
| TimeDeltaMs := LastSeen - FirstSeen
| TimeDeltaMs < 10000
| SpawnCount >= 2
| sort(SpawnCount, order=desc, limit=200)
| select([ComputerName, UserName, FileName, CommandLine, ParentBaseFileName, SpawnCount, TimeDeltaMs, FirstSeen, LastSeen, ObservedParentPIDs])Detects rapid consecutive process spawn events originating from a shell or scripting language interpreter within a 10-second window, indicating a possible double-fork or daemonize pattern being used to break the process tree. Shell and interpreter parents (bash, python, perl, etc.) are the most common delivery mechanism for double-fork malware payloads on Linux. A SpawnCount of 2 or more within a tight time window from the same TargetProcessId suggests the parent is repeatedly forking before exiting.
Data Sources
Required Tables
False Positives & Tuning
- Shell scripts used in CI/CD pipelines or deployment automation that launch multiple background worker processes in parallel (e.g., parallel test runners, concurrent service starters) will produce rapid back-to-back ProcessRollup2 events from a shell parent.
- Python or Perl-based job dispatchers and task queue workers (Celery, Gearman) that fork child workers from a persistent daemon process will generate clustered spawn events that match this detection pattern.
- Development tooling with hot-reload or watch functionality (nodemon, watchdog, entr) that restarts a subprocess immediately after detecting file changes will trigger repeated rapid process creation from an interpreter parent.
Other platforms for T1036.009
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 1Double Fork Process Tree Break
Expected signal: Auditd SYSCALL records for fork/clone syscalls (57/56) from bash. The resulting 'sleep 120' process will show PPID=1 in process listings. Syslog may record the orphaned process adoption.
- Test 2Daemon Syscall via Python
Expected signal: Auditd SYSCALL records for fork (57) and setsid (112) syscalls from python3. The grandchild python3 process will show PPID=1 and a new session ID (SID) in process status. /proc/<pid>/status will show PPid=1.
- Test 3Nohup Background Process Detachment
Expected signal: Auditd SYSCALL records for fork/clone from bash, followed by the nohup process. The sleep process may show PPID=1 after the parent shell exits. Process creation event from Sysmon for Linux (if deployed) shows nohup spawning sleep.
References (7)
- https://attack.mitre.org/techniques/T1036/009/
- https://0xjet.github.io/3OHA/2022/04/11/post.html
- https://sandflysecurity.com/blog/bpfdoor-an-evasive-linux-backdoor-technical-analysis/
- https://www.microsoft.com/en-us/security/blog/2022/05/19/rise-in-xorddos-a-deeper-look-at-the-stealthy-ddos-malware-targeting-linux-devices/
- https://man7.org/linux/man-pages/man2/fork.2.html
- https://man7.org/linux/man-pages/man3/daemon.3.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1036.009/T1036.009.md
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