RegAsm.EXE Execution Without CommandLine Flags or Files

Severity: low
Author: frack113
Source: upstream

Detects the execution of "RegAsm.exe" without a commandline flag or file, which might indicate potential process injection activity. Usually "RegAsm.exe" should point to a dedicated DLL file or call the help with the "/?" flag.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.009` System Binary Proxy Execution: Regsvcs/Regasm

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\RegAsm.exe'
OriginalFileName: RegAsm.exe

Stage 2: `all of selection_cli`

or:
CommandLine|endswith: RegAsm
CommandLine|endswith: RegAsm.exe
CommandLine|endswith: 'RegAsm.exe'''
CommandLine|endswith: 'RegAsm.exe"'

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`	ends_with	`RegAsm` `RegAsm.exe` `RegAsm.exe"` `RegAsm.exe'`
`Image`	ends_with	`\RegAsm.exe` corpus 3 (sigma 3)
`OriginalFileName`	eq	`RegAsm.exe` corpus 6 (sigma 6)