huntrule

Windows Registry Fax Device Provider ImageName changed to load external DLL

Alerts when Fax Device Providers\ImageName registry values change in a way consistent with DLL-loading persistence.

FreeUnreviewedSigmahighv1
title: Windows Registry Fax Device Provider ImageName changed to load external DLL
id: d00678fb-2600-4537-bd25-b93f9d99c8e2
status: test
description: This rule flags registry changes under the Fax device provider path where an ImageName value is set, indicating a possible Fax DLL load persistence mechanism upon service restart. Attackers may use this to cause a service to load a chosen DLL, helping maintain execution across restarts while blending into expected system component configuration. Detection relies on Windows registry set telemetry matching the targeted Fax provider subkeys and ImageName entries, while excluding cases where the ImageName points to %systemroot%\system32\fxst30.dll.
references:
  - https://twitter.com/dottor_morte/status/1544652325570191361
  - https://raw.githubusercontent.com/RiccardoAncarani/talks/master/F-Secure/unorthodox-lateral-movement.pdf
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_fax_dll_persistance.yml
author: frack113, Huntrule Team
date: 2022-07-17
modified: 2022-12-30
tags:
  - attack.persistence
  - attack.defense-impairment
  - attack.t1112
logsource:
  product: windows
  category: registry_set
detection:
  selection:
    TargetObject|contains|all:
      - \Software\Microsoft\Fax\Device Providers\
      - \ImageName
  filter:
    Details: "%systemroot%\\system32\\fxst30.dll"
  condition: selection and not filter
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 9e3357ba-09d4-4fbd-a7c5-ad6386314513
    type: derived

What it detects

This rule flags registry changes under the Fax device provider path where an ImageName value is set, indicating a possible Fax DLL load persistence mechanism upon service restart. Attackers may use this to cause a service to load a chosen DLL, helping maintain execution across restarts while blending into expected system component configuration. Detection relies on Windows registry set telemetry matching the targeted Fax provider subkeys and ImageName entries, while excluding cases where the ImageName points to %systemroot%\system32\fxst30.dll.

Known false positives

  • Unknown

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.