Sigma rule: Fax Service DLL Search Order Hijack

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-ca68ddaff20c, updated 2022-06-02T00:00:00.000Z.

Rule

Title
Fax Service DLL Search Order Hijack
Status
test
Level
high
Author
NVISO
Date
2020-05-04
Modified
2022-06-02
File
rules/windows/image_load/image_load_side_load_ualapi.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

The Fax service attempts to load ualapi.dll, which is non-existent. An attacker can then (side)load their own malicious DLL using this service.

Log source

product
windows
category
image_load

Detection

selection:
    Image|endswith: '\fxssvc.exe'
    ImageLoaded|endswith: 'ualapi.dll'
filter:
    ImageLoaded|startswith: 'C:\Windows\WinSxS\'
condition: selection and not filter

False positives (as the rule lists them)

  • Unlikely

Tags

  • attack.privilege-escalation
  • attack.persistence
  • attack.execution
  • attack.stealth
  • attack.t1574.001

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/windows/image_load/image_load_side_load_ualapi.yml

Sources and licences

  • SigmaHQ

    "Fax Service DLL Search Order Hijack" by NVISO (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/image_load/image_load_side_load_ualapi.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: Fax Service DLL Search Order Hijack",
entity page, dataset version ref-ca68ddaff20c, updated 2022-06-02T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/828af599-4c53-4ed2-ba4a-a9f835c434ea (accessed 2026-11-03).
Underlying source: SigmaHQ rule 828af599-4c53-4ed2-ba4a-a9f835c434ea, 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.