Detect Overwrite Process Arguments in CrowdStrike LogScale
Adversaries may modify a process's in-memory arguments to change its name in order to appear as a legitimate or benign process. On Linux, the operating system stores command-line arguments in the process's stack and passes them to the main() function as the argv array. The first element, argv[0], typically contains the process name or path. By default, the Linux /proc filesystem uses this value to represent the process name. The /proc/<PID>/cmdline file reflects the contents of this memory, and tools like ps use it to display process information. During runtime, adversaries can erase the memory used by all command-line arguments for a process, overwriting each argument string with null bytes, then write a spoofed string into the memory region previously occupied by argv[0] to mimic a benign command. This technique is used by BPFDoor, which overwrites its argv[0] with names resembling Linux system daemons such as /sbin/udevd -d, dbus-daemon --system, and avahi-daemon: chroot helper.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1036 Masquerading
- Sub-technique
- T1036.011 Overwrite Process Arguments
- Canonical reference
- https://attack.mitre.org/techniques/T1036/011/
LogScale Detection Query
#event_simpleName=ProcessRollup2
| CommandLine != ImageFileName
| regex(field=CommandLine, regex="^(/sbin/udevd|dbus-daemon|avahi-daemon|auditd|systemd-journald|/sbin/rpcbind|xinetd|crond|atd|acpid|smartd|irqbalance)", strict=false)
OR not regex(field=ImageFileName, regex="^(/usr/|/bin/|/sbin/|/lib/)", strict=false)
| eval is_daemon_claim := if(regex(CommandLine, "^(/sbin/udevd|dbus-daemon|avahi-daemon|auditd|systemd-journald|/sbin/rpcbind|xinetd|crond|atd|acpid|smartd|irqbalance)"), 1, 0)
| eval is_nonstandard_path := if(not regex(ImageFileName, "^(/usr/|/bin/|/sbin/|/lib/)"), 1, 0)
| eval suspicion_score := is_daemon_claim + is_nonstandard_path
| where suspicion_score > 0
| table([@timestamp, ComputerName, UserName, CommandLine, ImageFileName, ParentImageFileName, is_daemon_claim, is_nonstandard_path, suspicion_score])
| sort(field=suspicion_score, order=desc)
| sort(field=@timestamp, order=desc)Detects T1036.011 process argument overwriting using CrowdStrike Falcon ProcessRollup2 events on Linux endpoints. Compares the CommandLine field (reflecting argv[0] as presented) against the ImageFileName (actual binary on disk). Scores and surfaces events where the claimed name matches known Linux system daemon patterns or the real binary is outside standard system directories.
Data Sources
Required Tables
False Positives & Tuning
- Falcon sensor telemetry from custom Linux distributions where binaries are installed in non-standard paths (e.g., /opt/agent/) but present standard daemon names
- Interpreted language runtimes (Python, Ruby) that use setproctitle to display worker-specific names different from the interpreter binary path
- Legitimate penetration testing tooling or red team agents that mimic daemon names as part of an authorized exercise
Other platforms for T1036.011
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 1Overwrite argv[0] with Bash Process Substitution
Expected signal: Auditd EXECVE record with a0='/sbin/udevd -d' but exe pointing to /usr/bin/sleep (or /bin/sleep). The ps output shows the spoofed name. /proc/<PID>/cmdline shows '/sbin/udevd -d' while /proc/<PID>/exe symlinks to the actual sleep binary.
- Test 2Python prctl PR_SET_NAME Process Rename
Expected signal: Auditd SYSCALL record for prctl (syscall 157) with a0=15 (PR_SET_NAME) from python3. The /proc/<PID>/comm file will show 'avahi-daemon' while /proc/<PID>/exe still points to /usr/bin/python3. Process creation event shows python3 but ps output shows avahi-daemon.
- Test 3C Program argv[0] Overwrite and Fork (BPFDoor Simulation)
Expected signal: Auditd EXECVE record for /tmp/df00tech_argv_test. Fork SYSCALL (57) record. PROCTITLE record changing to hex-encoded '/sbin/udevd -d'. The child process shows PPID=1 (adopted by init) with args='/sbin/udevd -d' but /proc/<PID>/exe -> /tmp/df00tech_argv_test.
References (6)
- https://attack.mitre.org/techniques/T1036/011/
- 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/prctl.2.html
- https://man7.org/linux/man-pages/man5/proc_pid_cmdline.5.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1036.011/T1036.011.md
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