sigmahighHunting

Fax Service DLL Search Order Hijack

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.

MITRE ATT&CK

T1574.001

privilege-escalationpersistencedefense-evasion

Detection Query

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

Author

NVISO

Created

2020-05-04

Data Sources

windowsImage Load Events

Platforms

windows

References

https://windows-internals.com/faxing-your-way-to-system/

Tags

attack.privilege-escalationattack.persistenceattack.defense-evasionattack.t1574.001

Raw Content

title: Fax Service DLL Search Order Hijack
id: 828af599-4c53-4ed2-ba4a-a9f835c434ea
status: test
description: 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.
references:
    - https://windows-internals.com/faxing-your-way-to-system/
author: NVISO
date: 2020-05-04
modified: 2022-06-02
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.defense-evasion
    - attack.t1574.001
logsource:
    category: image_load
    product: windows
detection:
    selection:
        Image|endswith: '\fxssvc.exe'
        ImageLoaded|endswith: 'ualapi.dll'
    filter:
        ImageLoaded|startswith: 'C:\Windows\WinSxS\'
    condition: selection and not filter
falsepositives:
    - Unlikely
level: high