Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension

Severity: medium
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects potentially suspicious execution of the Regasm/Regsvcs utilities with an uncommon extension.

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'
Image|endswith: '\Regsvcs.exe'
OriginalFileName: RegAsm.exe
OriginalFileName: RegSvcs.exe

Stage 2: `all of selection_extension`

or:
CommandLine|contains: .dat
CommandLine|contains: .gif
CommandLine|contains: .jpeg
CommandLine|contains: .jpg
CommandLine|contains: .png
CommandLine|contains: .txt

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	`.dat` corpus 2 (sigma 2) `.gif` corpus 6 (sigma 6) `.jpeg` corpus 6 (sigma 6) `.jpg` corpus 7 (sigma 7) `.png` corpus 7 (sigma 7) `.txt` corpus 7 (sigma 7)
`Image`	ends_with	`\Regasm.exe` corpus 2 (sigma 2) `\Regsvcs.exe` corpus 2 (sigma 2)
`OriginalFileName`	eq	`RegAsm.exe` corpus 6 (sigma 6) `RegSvcs.exe` corpus 5 (sigma 5)