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Detection rules › Sigma

Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension

Status
test
Severity
medium
Log source
product windows, category process_creation
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

TacticTechniques
StealthT1218.009 System Binary Proxy Execution: Regsvcs/Regasm

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

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

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.

FieldKindValues
CommandLinematch
  • .dat corpus 3 (sigma 3)
  • .gif corpus 8 (sigma 8)
  • .jpeg corpus 6 (sigma 6)
  • .jpg corpus 7 (sigma 7)
  • .png corpus 7 (sigma 7)
  • .txt corpus 9 (sigma 9)
Imageends_with
  • \Regasm.exe corpus 9 (sigma 9)
  • \Regsvcs.exe corpus 8 (sigma 8)
OriginalFileNameeq
  • RegAsm.exe corpus 8 (sigma 6, elastic 1, splunk 1)
  • RegSvcs.exe corpus 7 (sigma 5, elastic 1, splunk 1)