Potential Regsvr32 Commandline Flag Anomaly

Hunt Hypothesis

Detects a potential command line flag anomaly related to “regsvr32” in which the “/i” flag is used without the “/n” which should be uncommon.

Detection Rule

Sigma (Original)

title: Potential Regsvr32 Commandline Flag Anomaly
id: b236190c-1c61-41e9-84b3-3fe03f6d76b0
status: test
description: Detects a potential command line flag anomaly related to "regsvr32" in which the "/i" flag is used without the "/n" which should be uncommon.
references:
    - https://twitter.com/sbousseaden/status/1282441816986484737?s=12
author: Florian Roth (Nextron Systems)
date: 2019-07-13
modified: 2024-03-13
tags:
    - attack.stealth
    - attack.t1218.010
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\regsvr32.exe'
        CommandLine|contains|windash: ' -i:'
    filter_main_flag:
        CommandLine|contains|windash: ' -n '
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Administrator typo might cause some false positives
level: medium

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessName endswith "\\regsvr32.exe" and (TargetProcessCommandLine contains " -i:" or TargetProcessCommandLine contains " /i:" or TargetProcessCommandLine contains " –i:" or TargetProcessCommandLine contains " —i:" or TargetProcessCommandLine contains " ―i:")) and (not(TargetProcessCommandLine contains " -n " or TargetProcessCommandLine contains " /n " or TargetProcessCommandLine contains " –n " or TargetProcessCommandLine contains " —n " or TargetProcessCommandLine contains " ―n "))

Required Data Sources

False Positive Guidance

• Administrator typo might cause some false positives

MITRE ATT&CK Context

• Technique: T1218.010 — T1218.010

References

• https://twitter.com/sbousseaden/status/1282441816986484737?s=12
• SigmaHQ Rule