Detect Overwrite Process Arguments in Splunk
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/
SPL Detection Query
index=linux_audit sourcetype=linux_audit type=EXECVE
| rex "a0=\"(?<claimed_name>[^\"]+)\""
| rex "exe=\"(?<actual_exe>[^\"]+)\""
| where isnotnull(claimed_name) AND isnotnull(actual_exe)
| where claimed_name!=actual_exe
| eval is_system_daemon_claim=if(match(claimed_name, "^(/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 match(actual_exe, "^(/usr/|/bin/|/sbin/|/lib/)"), 1, 0)
| eval SuspicionScore=is_system_daemon_claim + is_nonstandard_path
| where SuspicionScore > 0
| table _time, host, claimed_name, actual_exe, is_system_daemon_claim, is_nonstandard_path, SuspicionScore
| sort - SuspicionScore - _timeDetects argv[0] overwriting by comparing the claimed process name (a0 field in auditd EXECVE records) against the actual executable path (exe field). Assigns a suspicion score based on whether the claimed name matches a known BPFDoor-style daemon name AND whether the actual binary resides outside standard system paths. Higher scores indicate stronger confidence of malicious process argument manipulation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- BusyBox multi-call binary with symlink-based argv[0] on container/embedded systems
- Python/Perl applications using setproctitle() for operational process naming
- Shell scripts invoked via interpreter causing argv[0] path differences
- Snap/Flatpak packaged applications with wrapper script path mismatches
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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