Potential Ransomware Activity Using LegalNotice Message

Status: test
Severity: high
Log source: category registry_set, product windows
Author: frack113
Source: github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1491.001` Defacement: Internal Defacement

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 13: RegistryEvent (Value Set)

Rule body

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

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    TargetObject|contains:
        - '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeCaption'
        - '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeText'
    Details|contains:
        - 'encrypted'
        - 'Unlock-Password'
        - 'paying'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Details`	match	`Unlock-Password` `encrypted` `paying`	`field:"Details" kind:match`
`TargetObject`	match	`\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeCaption` `\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LegalNoticeText`	`field:"TargetObject" kind:match`