Detect Source in Elastic Security
Adversaries may abuse the shell built-in source command (or its dot notation equivalent '. ') to execute arbitrary scripts in the current shell context without requiring the target file to be marked executable. This technique is deprecated in ATT&CK but the underlying behavior remains relevant on Linux and macOS systems. The source command can load malicious functions into the current shell session, execute staged payloads from world-writable directories, or run scripts pulled from remote locations via process substitution (e.g., source <(curl ...)). Because the file does not need execute permissions (chmod +x), this technique can bypass permission-based detection controls. Adversaries commonly use this to execute payloads written to /tmp or /dev/shm, load malicious shell functions into memory, or chain with other techniques such as modifying .bashrc or .profile for persistence.
MITRE ATT&CK
- Tactic
- Execution
- Canonical reference
- https://attack.mitre.org/techniques/T1153/
Elastic Detection Query
process where host.os.type in ("linux", "macos") and
process.name in ("bash", "sh", "zsh", "dash", "ksh", "fish") and
(
process.command_line like~ "*source /*" or
process.command_line like~ "* . /*" or
process.command_line like~ "* . ~/*"
) and
(
process.command_line like~ "*source */tmp/*" or
process.command_line like~ "*source */dev/shm/*" or
process.command_line like~ "*source */var/tmp/*" or
process.command_line like~ "*source */run/*" or
process.command_line like~ "* . /tmp/*" or
process.command_line like~ "* . /dev/shm/*" or
process.command_line like~ "* . /var/tmp/*" or
process.command_line like~ "*source <(*" or
process.command_line like~ "*. <(*" or
process.command_line like~ "*source *.txt*" or
process.command_line like~ "*source *.log*" or
process.command_line like~ "*source *.conf*" or
process.command_line like~ "*source *.bak*" or
process.command_line like~ "*source *.tmp*" or
(process.command_line like~ "*base64*" and process.command_line like~ "*source *") or
process.parent.name in ("curl", "wget", "python", "python3", "perl", "ruby", "php", "nc", "ncat", "socat")
)Detects suspicious shell source command or dot notation (. ) abuse on Linux/macOS hosts. Flags sourcing from world-writable paths (/tmp, /dev/shm), process substitution patterns (source <(...)), execution of non-executable file types, base64-encoded payloads, and shells spawned by network utility parents such as curl or wget.
Data Sources
Required Tables
False Positives & Tuning
- System administrators sourcing environment setup scripts from /tmp during interactive maintenance or one-off debugging sessions
- CI/CD pipeline agents (Jenkins, GitLab Runner) that extract build scripts to /tmp and source them as part of normal job execution
- Developer dotfile managers (chezmoi, yadm) that source shell function libraries using non-.sh extensions such as .conf during shell initialisation
Other platforms for T1153
Testing Methodology
Validate this detection against 4 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 1Execute Non-Executable Script via source
Expected signal: auditd EXECVE record for bash with argument array including 'source /tmp/argus_payload.sh'. DeviceProcessEvents (MDE Linux): ProcessCommandLine containing 'source /tmp/argus_payload.sh', FileName=bash. File creation event for /tmp/argus_source_test.txt. The file permission check (644, no execute bit) is visible in the stat output confirming the bypass.
- Test 2Source via Dot Notation from /dev/shm
Expected signal: auditd EXECVE record: argument array for sh/bash containing '. /dev/shm/argus_stage.sh'. DeviceProcessEvents: ProcessCommandLine containing '. /dev/shm/argus_stage.sh'. File creation events for both the staged script in /dev/shm and the output file in /tmp.
- Test 3Fileless Execution via Process Substitution with source
Expected signal: auditd EXECVE record: bash with argument containing 'source <(echo ...)'. DeviceProcessEvents: ProcessCommandLine matching process substitution pattern. This is a fileless execution — no script file is created on disk, making file-based detections ineffective. The only durable telemetry is process creation and command line logging.
- Test 4Load Malicious Shell Function via source
Expected signal: auditd EXECVE records: (1) bash executing 'source /tmp/argus_func_payload.sh', (2) bash executing 'argus_backdoor test_argument' as a shell builtin invocation. DeviceProcessEvents: ProcessCommandLine showing both the source invocation and function call. Note that shell function calls may not generate separate process creation events since they execute in the current shell context — this is a key detection gap for function-based payloads.
References (8)
- https://attack.mitre.org/techniques/T1153/
- https://ss64.com/bash/source.html
- https://www.gnu.org/software/bash/manual/bash.html#Bourne-Shell-Builtins
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1153/T1153.md
- https://linux.die.net/man/8/auditd
- https://github.com/SigmaHQ/sigma/tree/master/rules/linux
- https://www.cyberciti.biz/faq/bash-source-command/
- https://learn.microsoft.com/en-us/defender-endpoint/linux-support-events
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