Execute Code with Pester.bat

Severity: medium
Author: Julia Fomina, oscd.community
Source: upstream

Detects code execution via Pester.bat (Pester - Powershell Modulte for testing)

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Defense Evasion	`T1216` System Script Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `powershell_module`

or:
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'
CommandLine|contains: Get-Help
CommandLine|contains: Pester

Stage 2: `cmd_execution`

CommandLine|contains: ';'
CommandLine|contains: pester
Image|endswith: '\cmd.exe'

Stage 3: `get_help`

or:
CommandLine|contains: '\?'
CommandLine|contains: help

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.

Field	Kind	Values
`CommandLine`	match	`;` corpus 2 (sigma 2) `Get-Help` `Pester` `\?` `help` `pester`
`Image`	ends_with	`\cmd.exe` corpus 92 (sigma 92) `\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140)