Suspicious PowerShell IEX Execution Patterns

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

Detects suspicious ways to run Invoke-Execution using IEX alias

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: `all of selection_combined_1`

or:
CommandLine|contains: ' | IEX (new'
CommandLine|contains: ' | IEX -Error'
CommandLine|contains: ' | IEX ;'
CommandLine|contains: ' | iex '
CommandLine|contains: ' | iex;'
CommandLine|contains: ' | iex}'
CommandLine|contains: ');IEX '
or:
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'

Stage 2: `all of selection_combined_2`

or:
CommandLine|contains: '.GetString([System.Convert]::'
CommandLine|contains: '::FromBase64String'

Stage 3: `selection_standalone`

or:
CommandLine|contains: ' | IEX | '
CommandLine|contains: ' | iex\"'
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	`\| IEX (new` `\| IEX -Error` `\| IEX ;` `\| IEX \|` `\| iex` `\| iex;` `\| iex\"` `\| iex}` `);IEX` `);iex $` `);iex($` `)\|iex;$` `.GetString([System.Convert]::` `::FromBase64String` corpus 2 (sigma 2)
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140)