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Detection rules › Sigma

Possible Exploitation of Exchange RCE CVE-2021-42321

Status
test
Severity
high
Log source
product windows, service msexchange-management
Author
Florian Roth (Nextron Systems), @testanull
Source
github.com/SigmaHQ/sigma

Detects log entries that appear in exploitation attempts against MS Exchange RCE CVE-2021-42321

MITRE ATT&CK coverage

TacticTechniques
Lateral MovementT1210 Exploitation of Remote Services

Rule body yaml

title: Possible Exploitation of Exchange RCE CVE-2021-42321
id: c92f1896-d1d2-43c3-92d5-7a5b35c217bb
status: test
description: Detects log entries that appear in exploitation attempts against MS Exchange RCE CVE-2021-42321
references:
    - https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321
author: 'Florian Roth (Nextron Systems), @testanull'
date: 2021-11-18
modified: 2022-07-12
tags:
    - attack.lateral-movement
    - attack.t1210
    - detection.emerging-threats
logsource:
    product: windows
    service: msexchange-management
    # warning: The 'data' field used in the detection section is the container for the event data as a whole. You may have to adapt the rule for your backend accordingly
detection:
    selection:
        EventID:
            - 6
            - 8
        Data|contains:
            - 'Cmdlet failed. Cmdlet Get-App, '
            - 'Task Get-App throwing unhandled exception: System.InvalidCastException:'
    condition: selection
falsepositives:
    - Unknown, please report false positives via https://github.com/SigmaHQ/sigma/issues
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    EventID:
        - 6
        - 8
    Data|contains:
        - 'Cmdlet failed. Cmdlet Get-App, '
        - 'Task Get-App throwing unhandled exception: System.InvalidCastException:'

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
Datamatch
  • Cmdlet failed. Cmdlet Get-App,
  • Task Get-App throwing unhandled exception: System.InvalidCastException: