Potentially Suspicious Execution Of Regasm/Regsvcs From Uncommon Location

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

Detects potentially suspicious execution of the Regasm/Regsvcs utilities from a potentially suspicious location

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_dir`

or:
CommandLine|contains: '\AppData\Local\Temp\'
CommandLine|contains: '\Microsoft\Windows\Start Menu\Programs\Startup\'
CommandLine|contains: '\PerfLogs\'
CommandLine|contains: '\Users\Public\'
CommandLine|contains: '\Windows\Temp\'

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	`\AppData\Local\Temp\` corpus 16 (sigma 16) `\Microsoft\Windows\Start Menu\Programs\Startup\` corpus 3 (sigma 3) `\PerfLogs\` corpus 2 (sigma 2) `\Users\Public\` corpus 17 (sigma 17) `\Windows\Temp\` corpus 10 (sigma 10)
`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)