Sigma rule: RegAsm.EXE Execution Without CommandLine Flags or Files

Rule

Title

RegAsm.EXE Execution Without CommandLine Flags or Files

Status

experimental

Level

low

Author

frack113

Date

2025-06-04

File

rules/windows/process_creation/proc_creation_win_regasm_no_flag_or_dll_execution.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the execution of "RegAsm.exe" without a commandline flag or file, which might indicate potential process injection activity.
Usually "RegAsm.exe" should point to a dedicated DLL file or call the help with the "/?" flag.

Log source

product

windows

category

process_creation

Detection

selection_img:
    - Image|endswith: '\RegAsm.exe'
    - OriginalFileName: 'RegAsm.exe'
selection_cli:
    CommandLine|endswith:
        - 'RegAsm'
        - 'RegAsm.exe'
        - 'RegAsm.exe"'
        - "RegAsm.exe'"
condition: all of selection_*

False positives (as the rule lists them)

• Legitimate use of Regasm by developers.

Tags

• attack.stealth
• attack.t1218.009

MITRE ATT&CK ids this rule names

• T1218.009

References

• https://www.mcafee.com/blogs/other-blogs/mcafee-labs/agent-teslas-unique-approach-vbs-and-steganography-for-delivery-and-intrusion/
• https://www.zscaler.fr/blogs/security-research/threat-actors-exploit-cve-2017-11882-deliver-agent-tesla
• https://learn.microsoft.com/en-us/dotnet/framework/tools/regasm-exe-assembly-registration-tool
• https://app.any.run/tasks/ea944b89-69d8-49c8-ac1f-5c76ad300db2
• https://www.joesandbox.com/analysis/1467354/0/html

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/process_creation/proc_creation_win_regasm_no_flag_or_dll_execution.yml