Sigma rule: Possible Exploitation of Exchange RCE CVE-2021-42321

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-f221ee9f82b8, updated 2022-07-12T00:00:00.000Z.

Rule

Title
Possible Exploitation of Exchange RCE CVE-2021-42321
Status
test
Level
high
Author
Florian Roth (Nextron Systems), @testanull
Date
2021-11-18
Modified
2022-07-12
File
rules-emerging-threats/2021/Exploits/CVE-2021-42321/win_exchange_cve_2021_42321.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

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

Log source

product
windows
service
msexchange-management

Detection

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

False positives (as the rule lists them)

  • Unknown, please report false positives via https://github.com/SigmaHQ/sigma/issues

Tags

  • attack.lateral-movement
  • attack.t1210
  • detection.emerging-threats

MITRE ATT&CK ids this rule names

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2021/Exploits/CVE-2021-42321/win_exchange_cve_2021_42321.yml

Sources and licences

  • SigmaHQ

    "Possible Exploitation of Exchange RCE CVE-2021-42321" by Florian Roth (Nextron Systems), @testanull (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2021/Exploits/CVE-2021-42321/win_exchange_cve_2021_42321.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Possible Exploitation of Exchange RCE CVE-2021-42321",
entity page, dataset version ref-f221ee9f82b8, updated 2022-07-12T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/c92f1896-d1d2-43c3-92d5-7a5b35c217bb (accessed 2026-11-03).
Underlying source: SigmaHQ rule c92f1896-d1d2-43c3-92d5-7a5b35c217bb, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.