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Detection rules › Sigma

Potential CVE-2021-40444 Exploitation Attempt

Status
test
Severity
high
Log source
product windows, category process_creation
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

TacticTechniques
ExecutionT1059 Command and Scripting Interpreter

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

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

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
CommandLineends_with\control.exe input.dll
CommandLineends_with\control.exe" input.dll

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
Imageends_with
  • \control.exe corpus 5 (sigma 5)
ParentImageends_with
  • \excel.exe corpus 8 (sigma 8)
  • \powerpnt.exe corpus 6 (sigma 6)
  • \winword.exe corpus 10 (sigma 10)