PowerShell Download and Execution Cradles

Severity: high
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects PowerShell download and execution cradles.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059` Command and Scripting Interpreter

Event coverage

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

Stages and Predicates

Stage 1: `all of selection_download`

or:
CommandLine|contains: '.DownloadFile('
CommandLine|contains: '.DownloadString('
CommandLine|contains: 'Invoke-RestMethod '
CommandLine|contains: 'Invoke-WebRequest '
CommandLine|contains: 'irm '
CommandLine|contains: 'iwr '

Stage 2: `all of selection_iex`

or:
CommandLine|contains: ';iex $'
CommandLine|contains: 'IEX ('
CommandLine|contains: 'IEX('
CommandLine|contains: 'IE`X'
CommandLine|contains: 'I`EX'
CommandLine|contains: 'I`E`X'
CommandLine|contains: Invoke-Expression
CommandLine|contains: 'iex '
CommandLine|contains: '| IEX'
CommandLine|contains: '|IEX '

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	`.DownloadFile(` corpus 3 (sigma 3) `.DownloadString(` corpus 3 (sigma 3) `;iex $` `IEX (` `IEX(` IE`X I`EX I`E`X `Invoke-Expression` corpus 2 (sigma 2) `Invoke-RestMethod` corpus 2 (sigma 2) `Invoke-WebRequest` corpus 4 (sigma 4) `iex` corpus 3 (sigma 3) `irm` corpus 3 (sigma 3) `iwr` corpus 8 (sigma 8) `\| IEX` `\|IEX`