Change the Fax Dll

Hunt Hypothesis

Detect possible persistence using Fax DLL load when service restart

Detection Rule

Sigma (Original)

title: Change the Fax Dll
id: 9e3357ba-09d4-4fbd-a7c5-ad6386314513
status: test
description: Detect possible persistence using Fax DLL load when service restart
references:
    - https://twitter.com/dottor_morte/status/1544652325570191361
    - https://raw.githubusercontent.com/RiccardoAncarani/talks/master/F-Secure/unorthodox-lateral-movement.pdf
author: frack113
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' # Windows 10
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where (RegistryKey endswith "\\Software\\Microsoft\\Fax\\Device Providers*" and RegistryKey contains "\\ImageName") and (not(RegistryValueData =~ "%systemroot%\\system32\\fxst30.dll"))

KQL (Microsoft 365 Defender)

DeviceRegistryEvents
| where (RegistryKey endswith "\\Software\\Microsoft\\Fax\\Device Providers*" and RegistryKey contains "\\ImageName") and (not(RegistryValueData =~ "%systemroot%\\system32\\fxst30.dll"))

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Persistence
• Technique: T1112 — T1112

References

• https://twitter.com/dottor_morte/status/1544652325570191361
• https://raw.githubusercontent.com/RiccardoAncarani/talks/master/F-Secure/unorthodox-lateral-movement.pdf
• SigmaHQ Rule