File Encoded To Base64 Via Certutil.EXE

Detects the execution of certutil with the "encode" flag to encode a file to base64. This can be abused by threat actors and attackers for data exfiltration

Sigma rule (View on GitHub)

 1title: File Encoded To Base64 Via Certutil.EXE
 2id: e62a9f0c-ca1e-46b2-85d5-a6da77f86d1a
 3status: test
 4description: Detects the execution of certutil with the "encode" flag to encode a file to base64. This can be abused by threat actors and attackers for data exfiltration
 5references:
 6    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
 7    - https://unit42.paloaltonetworks.com/new-babyshark-malware-targets-u-s-national-security-think-tanks/
 8    - https://lolbas-project.github.io/lolbas/Binaries/Certutil/
 9author: Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community, Nasreddine Bencherchali (Nextron Systems)
10date: 2019-02-24
11modified: 2024-03-05
12tags:
13    - attack.defense-evasion
14    - attack.t1027
15logsource:
16    category: process_creation
17    product: windows
18detection:
19    selection_img:
20        - Image|endswith: '\certutil.exe'
21        - OriginalFileName: 'CertUtil.exe'
22    selection_cli:
23        CommandLine|contains|windash: '-encode'
24    condition: all of selection_*
25falsepositives:
26    - As this is a general purpose rule, legitimate usage of the encode functionality will trigger some false positives. Apply additional filters accordingly
27level: medium

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