ExcaliburV103forgot

Hunt Hypothesis

This hypothesis targets the presence of the ExcaliburV103forgot YARA signature, which likely indicates the execution or persistence of a specific malware variant or script within the environment. Proactively hunting for this low-severity indicator allows the SOC team to identify dormant or early-stage infections before they escalate into more significant data exfiltration or lateral movement activities.

YARA Rule

rule ExcaliburV103forgot
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 00 00 00 00 60 E8 14 00 00 00 5D 81 ED 00 00 00 00 6A 45 E8 A3 00 00 00 68 00 00 00 00 E8 58 61 EB 39 }

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: A developer or DevOps engineer runs a local build script or CI/CD pipeline agent (e.g., Jenkins, GitLab Runner, or Azure DevOps Agent) that compiles a C/C++ project containing the specific string pattern or byte sequence targeted by the ExcaliburV103forgot YARA rule. This often happens in bin/, obj/, or build/ directories where intermediate artifacts or test binaries are generated.

  • Filter/Exclusion: Exclude paths matching *\build\*, *\bin\*, *\obj\*, or *\node_modules\* for user accounts tagged as ServiceAccount or DevTeam.

• Scenario: An IT administrator performs a manual patch deployment or software update using a tool like SCCM (System Center Configuration Manager) or Intune, which temporarily writes updated executable files to disk. If the updated binary (e.g., a Java JRE component, .NET Framework update, or third-party agent like CrowdStrike or Carbon Black) contains the specific signature, it may trigger the rule before the file is fully registered or hashed in the EDR database.

  • Filter/Exclusion: Exclude events where the parent process is ccmexec.exe, IntuneAgent.exe, or msiexec.exe, and the file age is less than 5 minutes.

• Scenario: A security team or application owner runs a known-good test binary or a custom internal utility (e.g., healthcheck.exe or diag_tool.exe) that was compiled with a specific compiler version or linker flag that inadvertently includes the byte pattern targeted by the rule. This is common when testing new internal tools in a staging environment.

  • Filter/Exclusion: Create a whitelist of known internal tool hashes (SHA256) or exclude files located in `C:\Program