CmdID

CmdID / Rules / Windows

File Encoded To Base64 Via Certutil.EXE

A Sigma rule for process creation on Windows, by Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community, Nasreddine Bencherchali (Nextron Systems).

medium 1 ATT&CK technique 1 program it names 2 everyday examples trip it

What it looks for

its detection, as SigmaHQ writes it
detection:
  selection_cli:
    CommandLine|contains|windash: '-encode'
  selection_img:
    - Image|endswith: '\certutil.exe'
    - OriginalFileName: 'CertUtil.exe'
  condition: all of selection_*

The rule’s detection, its selections and fields in order of name. The whole rule, with its references and false positives, is on SigmaHQ, by Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community, Nasreddine Bencherchali (Nextron Systems), under the Detection Rule License 1.1. CmdID evaluates it on a command line alone: a test on what a command line cannot show, such as the parent process or the user, is not met.

Command lines that trip it

everyday examples from tldr-pages, CC BY 4.0, each read by CmdID

Encode a file in hexadecimal on the page for certutil.exe

certutil -encodehex path\to\input_file path\to\output_fileIdentify

Encode a file to Base64 on the page for certutil.exe

certutil -encode path\to\input_file path\to\output_fileIdentify

The commands LOLBAS or GTFOBins documents for certutil.exe trip it too: each is on its program’s page, read by CmdID.

Programs and files it names

their pages here
certutil.exe

ATT&CK

the techniques it is tagged with
T1027Obfuscated Files or Information

Other rules for T1027 Obfuscated Files or Information

Decode Base64 Encoded Text · Decode Base64 Encoded Text -MacOs · Turla Group Commands May 2020 · File Decoded From Base64/Hex Via Certutil.EXE · Suspicious Download Via Certutil.EXE · Suspicious File Downloaded From Direct IP Via Certutil.EXE · Suspicious File Downloaded From File-Sharing Website Via Certutil.EXE · Suspicious File Encoded To Base64 Via Certutil.EXE · File In Suspicious Location Encoded To Base64 Via Certutil.EXE · Certificate Exported Via Certutil.EXE · Invoke-Obfuscation CLIP+ Launcher · Invoke-Obfuscation Obfuscated IEX Invocation