Excalibur103forgot

Hunt Hypothesis

This YARA rule targets specific memory or file artifacts associated with the “Excalibur103forgot” signature, potentially indicating the presence of a low-severity web shell, backdoor, or custom implant on Azure-hosted workloads. Proactively hunting for this indicator allows the SOC team to identify stealthy persistence mechanisms or initial footholds that may evade standard behavioral detections, ensuring early discovery of low-fidelity threats in the Azure Sentinel environment.

YARA Rule

rule Excalibur103forgot
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 00 00 00 00 60 E8 14 00 00 00 5D 81 ED 00 00 00 00 }

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 DevOps team deploys a custom Python-based health check script using the requests library to validate API endpoints, where the script source code or compiled bytecode contains the string “Excalibur103forgot” as a unique identifier or comment tag for internal tracking.
  • Filter/Exclusion: Exclude files located in specific application directories (e.g., C:\Apps\HealthCheck\) or exclude files with extensions .py, .pyc, or .whl if the rule is primarily targeting executable binaries.
• Scenario: An IT administrator uses a third-party backup or archiving tool (e.g., Veeam, Acronis) that creates temporary cache files or metadata logs containing the string “Excalibur103forgot” as a default session ID or license key fragment during a scheduled nightly backup job.
  • Filter/Exclusion: Exclude processes known to be backup services (e.g., veeam.exe, acronis.exe) or exclude files in temporary backup directories (e.g., C:\ProgramData\Backup\Temp\).
• Scenario: A software vendor’s installer (e.g., Adobe Creative Cloud, Microsoft Office) uses a temporary staging folder during installation or update, where a component file or log entry contains the string “Excalibur103forgot” as a build identifier or feature flag.
  • Filter/Exclusion: Exclude files in common installer temporary paths (e.g., C:\Windows\Temp\, C:\Users\<User>\AppData\Local\Temp\) or exclude processes associated with known installers (e.g., msiexec.exe, setup.exe from specific vendor directories).
• Scenario: A developer tests a new internal application feature by embedding the string “Excalibur103forgot” in a configuration file (e.g