Windows Process Creation: certutil.exe Encodes Files to Base64 in Suspicious Paths

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1027Obfuscated Files or Information
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule identifies executions of certutil.exe using the -encode option to base64-encode a file. It flags activity when the command line indicates the input file resides in paths commonly abused for staging or stealth, such as AppData, Temp, Desktop, PerfLogs, Public, Windows Temp, or the recycle bin. The detection relies on Windows process creation telemetry including the process image/original filename and the full command line.

Reporting behind it

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Windows Process Creation: certutil.exe Encodes Files to Base64 in Suspicious Paths

Pivot detection · T1027 · 9 related

Changelog

v2

v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-process-creation-certutil-exe-encode-writing-base64-from-suspicious-dire-82a6714f

title: "Windows Process Creation: certutil.exe Encodes Files to Base64 in Suspicious Paths"
id: 9d7f3ecb-075d-4b48-aab8-72fb9c8dbff5
related:
  - id: e62a9f0c-ca1e-46b2-85d5-a6da77f86d1a
    type: derived
  - id: 82a6714f-4899-4f16-9c1e-9a333544d4c3
    type: derived
status: test
description: This rule identifies executions of certutil.exe using the -encode option to base64-encode a file. It flags activity when the command line indicates the input file resides in paths commonly abused for staging or stealth, such as AppData, Temp, Desktop, PerfLogs, Public, Windows Temp, or the recycle bin. The detection relies on Windows process creation telemetry including the process image/original filename and the full command line.
references:
  - https://www.virustotal.com/gui/file/35c22725a92d5cb1016b09421c0a6cdbfd860fd4778b3313669b057d4a131cb7/behavior
  - https://www.virustotal.com/gui/file/427616528b7dbc4a6057ac89eb174a3a90f7abcf3f34e5a359b7a910d82f7a72/behavior
  - https://www.virustotal.com/gui/file/34de4c8beded481a4084a1fd77855c3e977e8ac643e5c5842d0f15f7f9b9086f/behavior
  - https://www.virustotal.com/gui/file/4abe1395a09fda06d897a9c4eb247278c1b6cddda5d126ce5b3f4f499e3b8fa2/behavior
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_certutil_encode_susp_location.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2023-05-15
modified: 2024-03-05
tags:
  - attack.stealth
  - attack.t1027
logsource:
  category: process_creation
  product: windows
detection:
  selection_img:
    - Image|endswith: \certutil.exe
    - OriginalFileName: CertUtil.exe
  selection_cli:
    CommandLine|contains|windash: -encode
  selection_extension:
    CommandLine|contains:
      - \AppData\Roaming\
      - \Desktop\
      - \Local\Temp\
      - \PerfLogs\
      - \Users\Public\
      - \Windows\Temp\
      - $Recycle.Bin
  condition: all of selection_*
falsepositives:
  - Unknown
level: high
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_certutil_encode_susp_location/info.yml
license: DRL-1.1

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