Detection rules › Splunk
Suspicious PowerShell Parameter Substring (Windows Event Log)
Threat actors may use obfuscated and truncated PowerShell execution arguments to evade detection, leveraging PowerShell's parameter binding functionality that allows partial matching of command-line arguments. This use case detects process executions containing substrings for commonly abused PowerShell parameters.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1059.001 Command and Scripting Interpreter: PowerShell |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '30388.54457'
title: Suspicious PowerShell Parameter Substring
description: Threat actors may use obfuscated and truncated PowerShell execution arguments
to evade detection, leveraging PowerShell's parameter binding functionality that
allows partial matching of command-line arguments. This use case detects process
executions containing substrings for commonly abused PowerShell parameters.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
"EventID>4688<" OR Type=Process) ("cmd.exe" OR "pwsh.exe" OR "powershell.exe") ("
-windowstyl " OR " -windowsty " OR " -windowst " OR " -windows " OR " -windo " OR
" -wind " OR " -win " OR " -wi") OR (" -executionpolic " OR " -executionpoli " OR
" -executionpol " OR " -executionpo " OR " -executionp " OR " -execution " OR "
-executio " OR " -executi " OR " -execut " OR " -execu " OR " -exec " OR " -exe
" OR " -ex") OR " -NoPr " OR " -NoPro " OR " -NoProf " OR " -NoProfi " OR " -NoProfil
" OR " -nonin " OR " -nonint " OR " -noninte " OR " -noninter " OR " -nonintera
" OR " -noninterac " OR " -noninteract " OR " -noninteracti " OR " -noninteractiv
" OR " -ec " OR " -encodedComman " OR " -encodedComma " OR " -encodedComm " OR "
-encodedCom " OR " -encodedCo " OR " -encodedC " OR " -encoded " OR " -encode "
OR " -encod " OR " -enco " OR " -en " OR (" /windowstyle " OR " /windowstyl " OR
" /windowsty " OR " /windowst " OR " /windows " OR " /windo " OR " /wind " OR "
/win " OR " /wi") OR (" /executionpolic " OR " /executionpoli " OR " /executionpol
" OR " /executionpo " OR " /executionp " OR " /execution " OR " /executio " OR "
/executi " OR " /execut " OR " /execu " OR " /exec " OR " /exe " OR " /ex") OR "
/NoPr " OR " /NoPro " OR " /NoProf " OR " /NoProfi " OR " /NoProfil " OR " /nonin
" OR " /nonint " OR " /noninte " OR " /noninter " OR " /nonintera " OR " /noninterac
" OR " /noninteract " OR " /noninteracti " OR " /noninteractiv " OR " /ec " OR "
/encodedComman " OR " /encodedComma " OR " /encodedComm " OR " /encodedCom " OR
" /encodedCo " OR " /encodedC " OR " /encoded " OR " /encode " OR " /encod " OR
" /enco " OR " /en" | regex process="(?i)\s(-|\/)(win?d?o?w?s?t?y?l?\s+hi?d?d?e?|windowstyle\s+h\s|NoPro?f?i?l?\s|nonint?e?r?a?c?t?i?v?\s|enc?o?d?e?d?C?o?m?m?a?n?\s|((exe?c?u?t?i?o?n?p?o?l?i?c?)|ep)\s+(bypass)?|ec\s)"
| table _time, host, user user, process, process_*, parent_* | bin span=1s | stats
values(*) as * by _time, host '
techniques:
- execution:command and scripting interpreter:powershell
technique_id:
- T1059.001
data_category:
- Process command-line parameters
- Windows event logs
references:
- http://www.danielbohannon.com/blog-1/2017/3/12/powershell-execution-argument-obfuscation-how-it-can-make-detection-easier
- https://github.com/SigmaHQ/sigma/blob/c0332a9d96f6c7804fcc85dd706caed889446a62/rules/windows/process_creation/proc_creation_win_powershell_susp_parameter_variation.yml
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR "EventID>4688<" OR Type=Process) ("cmd.exe" OR "pwsh.exe" OR "powershell.exe") (" -windowstyl " OR " -windowsty " OR " -windowst " OR " -windows " OR " -windo " OR " -wind " OR " -win " OR " -wi") OR (" -executionpolic " OR " -executionpoli " OR " -executionpol " OR " -executionpo " OR " -executionp " OR " -execution " OR " -executio " OR " -executi " OR " -execut " OR " -execu " OR " -exec " OR " -exe " OR " -ex") OR " -NoPr " OR " -NoPro " OR " -NoProf " OR " -NoProfi " OR " -NoProfil " OR " -nonin " OR " -nonint " OR " -noninte " OR " -noninter " OR " -nonintera " OR " -noninterac " OR " -noninteract " OR " -noninteracti " OR " -noninteractiv " OR " -ec " OR " -encodedComman " OR " -encodedComma " OR " -encodedComm " OR " -encodedCom " OR " -encodedCo " OR " -encodedC " OR " -encoded " OR " -encode " OR " -encod " OR " -enco " OR " -en " OR (" /windowstyle " OR " /windowstyl " OR " /windowsty " OR " /windowst " OR " /windows " OR " /windo " OR " /wind " OR " /win " OR " /wi") OR (" /executionpolic " OR " /executionpoli " OR " /executionpol " OR " /executionpo " OR " /executionp " OR " /execution " OR " /executio " OR " /executi " OR " /execut " OR " /execu " OR " /exec " OR " /exe " OR " /ex") OR " /NoPr " OR " /NoPro " OR " /NoProf " OR " /NoProfi " OR " /NoProfil " OR " /nonin " OR " /nonint " OR " /noninte " OR " /noninter " OR " /nonintera " OR " /noninterac " OR " /noninteract " OR " /noninteracti " OR " /noninteractiv " OR " /ec " OR " /encodedComman " OR " /encodedComma " OR " /encodedComm " OR " /encodedCom " OR " /encodedCo " OR " /encodedC " OR " /encoded " OR " /encode " OR " /encod " OR " /enco " OR " /en"
Stage 2: regex
| regex process="(?i)\s(-|\/)(win?d?o?w?s?t?y?l?\s+hi?d?d?e?|windowstyle\s+h\s|NoPro?f?i?l?\s|nonint?e?r?a?c?t?i?v?\s|enc?o?d?e?d?C?o?m?m?a?n?\s|((exe?c?u?t?i?o?n?p?o?l?i?c?)|ep)\s+(bypass)?|ec\s)"
Stage 3: table
| table _time, host, user user, process, process_*, parent_*
Stage 4: bucket
| bin span=1s
Stage 5: stats
| stats values(*) as * by _time, host
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "EventID>4688<" |
| 1 | "cmd.exe" |
| 1 | "pwsh.exe" |
| 1 | "powershell.exe" |
| 1 | " -windowstyl " |
| 1 | " -windowsty " |
| 1 | " -windowst " |
| 1 | " -windows " |
| 1 | " -windo " |
| 1 | " -wind " |
| 1 | " -win " |
| 1 | " -wi" |
| 1 | " -executionpolic " |
| 1 | " -executionpoli " |
| 1 | " -executionpol " |
| 1 | " -executionpo " |
| 1 | " -executionp " |
| 1 | " -execution " |
| 1 | " -executio " |
| 1 | " -executi " |
| 1 | " -execut " |
| 1 | " -execu " |
| 1 | " -exec " |
| 1 | " -exe " |
| 1 | " -ex" |
| 1 | " -NoPr " |
| 1 | " -NoPro " |
| 1 | " -NoProf " |
| 1 | " -NoProfi " |
| 1 | " -NoProfil " |
| 1 | " -nonin " |
| 1 | " -nonint " |
| 1 | " -noninte " |
| 1 | " -noninter " |
| 1 | " -nonintera " |
| 1 | " -noninterac " |
| 1 | " -noninteract " |
| 1 | " -noninteracti " |
| 1 | " -noninteractiv " |
| 1 | " -ec " |
| 1 | " -encodedComman " |
| 1 | " -encodedComma " |
| 1 | " -encodedComm " |
| 1 | " -encodedCom " |
| 1 | " -encodedCo " |
| 1 | " -encodedC " |
| 1 | " -encoded " |
| 1 | " -encode " |
| 1 | " -encod " |
| 1 | " -enco " |
| 1 | " -en " |
| 1 | " /windowstyle " |
| 1 | " /windowstyl " |
| 1 | " /windowsty " |
| 1 | " /windowst " |
| 1 | " /windows " |
| 1 | " /windo " |
| 1 | " /wind " |
| 1 | " /win " |
| 1 | " /wi" |
| 1 | " /executionpolic " |
| 1 | " /executionpoli " |
| 1 | " /executionpol " |
| 1 | " /executionpo " |
| 1 | " /executionp " |
| 1 | " /execution " |
| 1 | " /executio " |
| 1 | " /executi " |
| 1 | " /execut " |
| 1 | " /execu " |
| 1 | " /exec " |
| 1 | " /exe " |
| 1 | " /ex" |
| 1 | " /NoPr " |
| 1 | " /NoPro " |
| 1 | " /NoProf " |
| 1 | " /NoProfi " |
| 1 | " /NoProfil " |
| 1 | " /nonin " |
| 1 | " /nonint " |
| 1 | " /noninte " |
| 1 | " /noninter " |
| 1 | " /nonintera " |
| 1 | " /noninterac " |
| 1 | " /noninteract " |
| 1 | " /noninteracti " |
| 1 | " /noninteractiv " |
| 1 | " /ec " |
| 1 | " /encodedComman " |
| 1 | " /encodedComma " |
| 1 | " /encodedComm " |
| 1 | " /encodedCom " |
| 1 | " /encodedCo " |
| 1 | " /encodedC " |
| 1 | " /encoded " |
| 1 | " /encode " |
| 1 | " /encod " |
| 1 | " /enco " |
| 1 | " /en" |