PowerShell Download Pattern

Severity: medium
Author: Florian Roth (Nextron Systems), oscd.community, Jonhnathan Ribeiro
Source: upstream

Detects a Powershell process that contains download commands in its command line string

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\powershell.exe'
Image|endswith: '\powershell_ise.exe'
Image|endswith: '\pwsh.exe'
OriginalFileName: PowerShell.EXE
OriginalFileName: PowerShell_ISE.EXE
OriginalFileName: pwsh.dll

Stage 2: `all of selection_cli`

or:
CommandLine|contains: 'file('
CommandLine|contains: 'string('
CommandLine|contains: download
CommandLine|contains: 'net.webclient).'
CommandLine|contains: new-object

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	`download` `file(` `net.webclient).` `new-object` corpus 3 (sigma 3) `string(`
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\powershell_ise.exe` corpus 27 (sigma 27) `\pwsh.exe` corpus 140 (sigma 140)
`OriginalFileName`	eq	`PowerShell.EXE` corpus 64 (sigma 60, splunk 4) `PowerShell_ISE.EXE` corpus 6 (sigma 6) `pwsh.dll` corpus 72 (sigma 68, splunk 4)