Potential Ransomware Activity Using LegalNotice Message

Hunt Hypothesis

Detect changes to the “LegalNoticeCaption” or “LegalNoticeText” registry values where the message set contains keywords often used in ransomware ransom messages

Detection Rule

Sigma (Original)

title: Potential Ransomware Activity Using LegalNotice Message
id: 8b9606c9-28be-4a38-b146-0e313cc232c1
status: test
description: Detect changes to the "LegalNoticeCaption" or "LegalNoticeText" registry values where the message set contains keywords often used in ransomware ransom messages
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/5c1e6f1b4fafd01c8d1ece85f510160fc1275fbf/atomics/T1491.001/T1491.001.md
author: frack113
date: 2022-12-11
modified: 2023-08-17
tags:
    - attack.impact
    - attack.t1491.001
logsource:
    product: windows
    category: registry_set
detection:
    selection:
        TargetObject|contains:
            - '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeCaption'
            - '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeText'
        Details|contains:
            - 'encrypted'
            - 'Unlock-Password'
            - 'paying'
    condition: selection
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where (RegistryKey contains "\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\LegalNoticeCaption" or RegistryKey contains "\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\LegalNoticeText") and (RegistryValueData contains "encrypted" or RegistryValueData contains "Unlock-Password" or RegistryValueData contains "paying")

KQL (Microsoft 365 Defender)

DeviceRegistryEvents
| where (RegistryKey contains "\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\LegalNoticeCaption" or RegistryKey contains "\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\LegalNoticeText") and (RegistryValueData contains "encrypted" or RegistryValueData contains "Unlock-Password" or RegistryValueData contains "paying")

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Impact
• Technique: T1491.001 — T1491.001

References

• https://github.com/redcanaryco/atomic-red-team/blob/5c1e6f1b4fafd01c8d1ece85f510160fc1275fbf/atomics/T1491.001/T1491.001.md
• SigmaHQ Rule