Potential CVE-2021-40444 Exploitation Attempt

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Florian Roth (Nextron Systems), @neonprimetime
Source: github.com/SigmaHQ/sigma

Detects potential exploitation of CVE-2021-40444 via suspicious process patterns seen in in-the-wild exploitations

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059` Command and Scripting Interpreter

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Potential CVE-2021-40444 Exploitation Attempt
id: 894397c6-da03-425c-a589-3d09e7d1f750
status: test
description: Detects potential exploitation of CVE-2021-40444 via suspicious process patterns seen in in-the-wild exploitations
references:
    - https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
    - https://twitter.com/neonprimetime/status/1435584010202255375
    - https://www.joesandbox.com/analysis/476188/1/iochtml
author: Florian Roth (Nextron Systems), @neonprimetime
date: 2021-09-08
modified: 2023-02-04
tags:
    - attack.execution
    - attack.t1059
    - cve.2021-40444
    - detection.emerging-threats
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\control.exe'
        ParentImage|endswith:
            - '\winword.exe'
            - '\powerpnt.exe'
            - '\excel.exe'
    filter:
        CommandLine|endswith:
            - '\control.exe input.dll'
            - '\control.exe" input.dll'
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    Image|endswith: '\control.exe'
    ParentImage|endswith:
        - '\winword.exe'
        - '\powerpnt.exe'
        - '\excel.exe'

Stage 2: `not filter`

filter:
    CommandLine|endswith:
        - '\control.exe input.dll'
        - '\control.exe" input.dll'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	ends_with	`\control.exe input.dll`	`excludes:CommandLine` `field:"CommandLine" value:"\control.exe input.dll"`
`CommandLine`	ends_with	`\control.exe" input.dll`	`excludes:CommandLine`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\control.exe` corpus 5 (sigma 5)	`field:"Image" kind:ends_with value:"\control.exe"`
`ParentImage`	ends_with	`\excel.exe` corpus 8 (sigma 8) `\powerpnt.exe` corpus 6 (sigma 6) `\winword.exe` corpus 10 (sigma 10)	`field:"ParentImage" kind:ends_with`