Sigma rule: File Decoded From Base64/Hex Via Certutil.EXE

Rule

Title

File Decoded From Base64/Hex Via Certutil.EXE

Status

test

Level

high

Author

Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community

Date

2023-02-15

Modified

2025-06-04

File

rules/windows/process_creation/proc_creation_win_certutil_decode.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the execution of certutil with either the "decode" or "decodehex" flags to decode base64 or hex encoded files. This can be abused by attackers to decode an encoded payload before execution

Log source

product

windows

category

process_creation

Detection

selection_img:
    - Image|endswith: '\certutil.exe'
    - OriginalFileName: 'CertUtil.exe'
selection_cli:
    CommandLine|contains|windash:
        - '-decode ' # Decode Base64
        - '-decodehex ' # Decode Hex
condition: all of selection_*

False positives (as the rule lists them)

• Unknown

Tags

• attack.stealth
• attack.t1027

MITRE ATT&CK ids this rule names

• T1027

References

• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
• https://unit42.paloaltonetworks.com/new-babyshark-malware-targets-u-s-national-security-think-tanks/
• https://news.sophos.com/en-us/2021/04/13/compromised-exchange-server-hosting-cryptojacker-targeting-other-exchange-servers/
• https://twitter.com/JohnLaTwC/status/835149808817991680
• https://learn.microsoft.com/en-us/archive/blogs/pki/basic-crl-checking-with-certutil
• https://lolbas-project.github.io/lolbas/Binaries/Certutil/

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_certutil_decode.yml