Detect Break Process Trees in Sumo Logic CSE
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/
Sumo Detection Query
_sourceCategory=linux/audit type=SYSCALL (syscall=57 OR syscall=58 OR syscall=56)
| parse "pid=* " as pid
| parse "ppid=* " as ppid
| parse regex "exe=\"(?<exe>[^\"]+)\""
| parse "auid=* " as auid
| parse "syscall=* " as syscall
| where !(exe matches "/usr/sbin/*" OR exe matches "/lib/systemd/*" OR exe matches "/usr/lib/systemd/*")
| timeslice 5s
| count as ForkCount by _timeslice, _sourceHost, pid, ppid, auid, exe
| where ForkCount >= 2
| sort by ForkCount desc
| fields _timeslice, _sourceHost, pid, ppid, auid, exe, ForkCountDetects the double-fork process tree breaking technique by identifying hosts where the same process ID invokes fork (57), vfork (58), or clone (56) syscalls at least twice within a 5-second timeslice using Linux auditd data. This is the canonical signature of adversaries using the double-fork idiom or daemon() call to orphan a payload and cause it to be adopted by init (PID 1), bypassing process tree-based correlation in security tooling.
Data Sources
Required Tables
False Positives & Tuning
- Application servers using pre-fork worker models (Apache httpd prefork MPM, Puma, Unicorn, Gunicorn) legitimately invoke fork() multiple times during startup or hot reload, producing ForkCount values well above the threshold of 2.
- Containerized workloads using runc or crun as container runtime may generate clustered fork/clone syscall events during container creation and initialization sequences that match this pattern.
- Security scanning tools or vulnerability assessment frameworks that enumerate or probe processes via forked subprocesses will generate elevated fork counts across scanning hosts.
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
Unlock Pro Content
Get the full detection package for T1036.009 including response playbook, investigation guide, and atomic red team tests.