Sigma rule: Unsigned DLL Loaded by Windows Utility

Rule

Title

Unsigned DLL Loaded by Windows Utility

Status

test

Level

medium

Author

Swachchhanda Shrawan Poudel

Date

2024-02-28

Modified

2025-10-07

File

rules/windows/image_load/image_load_susp_unsigned_dll.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects windows utilities loading an unsigned or untrusted DLL.
Adversaries often abuse those programs to proxy execution of malicious code.

Log source

product

windows

category

image_load

Detection

selection:
    Image|endswith:
        # Note: Add additional utilities that allow the loading of DLLs
        - '\InstallUtil.exe'
        - '\RegAsm.exe'
        - '\RegSvcs.exe'
        - '\regsvr32.exe'
        - '\rundll32.exe'
filter_main_signed:
    Signed: 'true'
filter_main_sig_status:
    SignatureStatus:
        - 'errorChaining'
        - 'errorCode_endpoint'
        - 'errorExpired'
        - 'trusted'
        - 'Valid'
filter_main_signed_null:
    Signed: null
filter_main_signed_empty:
    Signed:
        - ''
        - '-'
filter_main_sig_status_null:
    SignatureStatus: null
filter_main_sig_status_empty:
    SignatureStatus:
        - ''
        - '-'
filter_main_windows_installer:
    Image:
        - 'C:\Windows\SysWOW64\rundll32.exe'
        - 'C:\Windows\System32\rundll32.exe'
    ImageLoaded|startswith: 'C:\Windows\Installer\'
    ImageLoaded|endswith:
        - '.tmp-\Microsoft.Deployment.WindowsInstaller.dll'
        - '.tmp-\Avira.OE.Setup.CustomActions.dll'
filter_main_assembly:
    Image|startswith:
        - 'C:\Windows\SysWOW64\'
        - 'C:\Windows\System32\'
        - 'C:\Windows\Microsoft.NET\Framework64'
    Image|endswith: '\RegAsm.exe'
    ImageLoaded|endswith: '.dll'
    ImageLoaded|startswith: 'C:\Windows\assembly\NativeImages'
filter_optional_klite_codec:
    Image:
        - 'C:\Windows\SysWOW64\regsvr32.exe'
        - 'C:\Windows\System32\regsvr32.exe'
    ImageLoaded|startswith:
        - 'C:\Program Files (x86)\K-Lite Codec Pack\'
        - 'C:\Program Files\K-Lite Codec Pack\'
condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*

False positives (as the rule lists them)

• Unknown

Tags

• attack.stealth
• attack.t1218.011
• attack.t1218.010

MITRE ATT&CK ids this rule names

• T1218.010
• T1218.011

References

• https://www.elastic.co/security-labs/Hunting-for-Suspicious-Windows-Libraries-for-Execution-and-Evasion
• https://akhere.hashnode.dev/hunting-unsigned-dlls-using-kql
• https://unit42.paloaltonetworks.com/unsigned-dlls/?web_view=true

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_susp_unsigned_dll.yml