Suspicious PowerShell Download and Execute Pattern

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

Detects suspicious PowerShell download patterns that are often used in malicious scripts, stagers or downloaders (make sure that your backend applies the strings case-insensitive)

MITRE ATT&CK coverage

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

Event coverage

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

Stages and Predicates

Stage 1: `selection`

or:
CommandLine|contains: ' -c (New-Object System.Net.WebClient).DownloadFile('
CommandLine|contains: ' -command (New-Object System.Net.WebClient).DownloadFile('
CommandLine|contains: 'IEX ((New-Object Net.WebClient).DownloadString'
CommandLine|contains: 'IEX (New-Object Net.WebClient).DownloadString'
CommandLine|contains: 'IEX((New-Object Net.WebClient).DownloadString'
CommandLine|contains: 'IEX(New-Object Net.WebClient).DownloadString'

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.