PESpinv11Cyberbob

Hunt Hypothesis

This hypothesis targets the execution of the Cyberbob malware variant, a low-severity threat that may indicate an initial foothold or lateral movement attempt within the environment. Proactively hunting for this specific YARA signature allows the SOC team to identify compromised hosts early, potentially uncovering stealthy persistence mechanisms or data staging activities before they escalate to higher-impact attacks.

YARA Rule

rule PESpinv11Cyberbob
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 7D DE 46 00 0B E4 74 9E 75 01 C7 81 73 04 D7 7A F7 2F 81 73 19 77 00 43 B7 F6 C3 6B B7 00 00 F9 FF E3 C9 C2 08 00 A3 68 72 01 FF 5D 33 C9 41 E2 17 EB 07 EA EB 01 EB EB 0D FF }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Execution of the CyberChef web application’s local desktop client or its associated Python-based CLI tools (cyberchef-cli) during manual data conversion tasks by application support teams.
  • Filter/Exclusion: Exclude processes where the parent process is python.exe or cyberchef-cli.exe and the command line contains arguments related to input/output file paths (e.g., --input, --output) or specific transformation modules (e.g., ROT13, Base64).
• Scenario: Running Jupyter Notebook or JupyterLab kernels that load the cyberchef Python package for automated log parsing or data enrichment in data science pipelines.
  • Filter/Exclusion: Exclude events where the process name is jupyter-notebook.exe or jupyter-lab.exe and the working directory is within the organization’s standard data science environment paths (e.g., C:\Users\Public\Jupyter\ or D:\DataScience\Projects\).
• Scenario: Scheduled maintenance jobs for GitLab CI/CD or Jenkins pipelines that execute build scripts invoking CyberChef’s API or local binaries for artifact validation (e.g., checking for hardcoded secrets via CyberChef transformations).
  • Filter/Exclusion: Exclude processes spawned by jenkins.exe, gitlab-runner.exe, or node.exe (for npm-based runners) where the process tree includes a parent process with a name matching *runner*, *jenkins*, or *ci* and the execution path is within the CI/CD workspace directory (e.g., C:\Jenkins\workspace\ or C:\gitlab-runner\builds\).
• Scenario: Execution of VS Code extensions or IntelliJ plugins that integrate