Sigma rule: Potential CVE-2021-26857 Exploitation Attempt

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-7faa53a92532, updated 2023-02-07T00:00:00.000Z.

Rule

Title
Potential CVE-2021-26857 Exploitation Attempt
Status
stable
Level
high
Author
Bhabesh Raj
Date
2021-03-03
Modified
2023-02-07
File
rules-emerging-threats/2021/Exploits/CVE-2021-26857/proc_creation_win_exploit_cve_2021_26857_msexchange.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects possible successful exploitation for vulnerability described in CVE-2021-26857 by looking for | abnormal subprocesses spawning by Exchange Server's Unified Messaging service

Log source

product
windows
category
process_creation

Detection

selection:
    ParentImage|endswith: '\UMWorkerProcess.exe'
filter:
    Image|endswith:
        - 'wermgr.exe'
        - 'WerFault.exe'
condition: selection and not filter

False positives (as the rule lists them)

  • Unknown

Tags

  • attack.t1203
  • attack.execution
  • cve.2021-26857
  • detection.emerging-threats

CVEs this rule names

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-2021-26857/proc_creation_win_exploit_cve_2021_26857_msexchange.yml

Sources and licences

  • SigmaHQ

    "Potential CVE-2021-26857 Exploitation Attempt" by Bhabesh Raj (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2021/Exploits/CVE-2021-26857/proc_creation_win_exploit_cve_2021_26857_msexchange.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: Potential CVE-2021-26857 Exploitation Attempt",
entity page, dataset version ref-7faa53a92532, updated 2023-02-07T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/cd479ccc-d8f0-4c66-ba7d-e06286f3f887 (accessed 2026-11-03).
Underlying source: SigmaHQ rule cd479ccc-d8f0-4c66-ba7d-e06286f3f887, 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.