Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

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

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension
id: e9f8f8cc-07cc-4e81-b724-f387db9175e4
related:
    - id: cc368ed0-2411-45dc-a222-510ace303cb2
      type: derived
status: test
description: Detects potentially suspicious execution of the Regasm/Regsvcs utilities with an uncommon extension.
references:
    - https://www.fortiguard.com/threat-signal-report/4718?s=09
    - https://lolbas-project.github.io/lolbas/Binaries/Regasm/
    - https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-02-13
tags:
    - attack.stealth
    - attack.t1218.009
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\Regsvcs.exe'
              - '\Regasm.exe'
        - OriginalFileName:
              - 'RegSvcs.exe'
              - 'RegAsm.exe'
    selection_extension:
        CommandLine|contains:
            # Note: Add more potentially uncommon extensions
            - '.dat'
            - '.gif'
            - '.jpeg'
            - '.jpg'
            - '.png'
            - '.txt'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

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

Stage 2: `selection_extension`

selection_extension:
    CommandLine|contains:
        - '.dat'
        - '.gif'
        - '.jpeg'
        - '.jpg'
        - '.png'
        - '.txt'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`.dat` corpus 4 (sigma 3, elastic 1) `.gif` corpus 9 (sigma 8, elastic 1) `.jpeg` corpus 7 (sigma 6, elastic 1) `.jpg` corpus 8 (sigma 7, elastic 1) `.png` corpus 8 (sigma 7, elastic 1) `.txt` corpus 9 (sigma 9)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\Regasm.exe` corpus 9 (sigma 9) `\Regsvcs.exe` corpus 8 (sigma 8)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`RegAsm.exe` corpus 14 (elastic 7, sigma 6, splunk 1) `RegSvcs.exe` corpus 13 (elastic 7, sigma 5, splunk 1)	`field:"OriginalFileName" kind:eq`

Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_extension

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_extension`