eXcalibur v103 forgotus h

Hunt Hypothesis

This hypothesis targets the presence of the eXcalibur v103 “forgotus” YARA signature, which indicates a specific variant of the eXcalibur infostealer often used to harvest credentials and browser data from compromised endpoints. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify early-stage infostealer infections that may be evading traditional behavioral detections, enabling rapid containment before data exfiltration occurs.

YARA Rule

rule eXcalibur_v103_forgotus_h: PEiD
{
    strings:
        $a = { 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 20 45 78 63 61 6C 69 62 75 72 20 28 63 29 20 62 79 20 66 6F 72 67 6F 74 2F 75 53 2F 44 46 43 47 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 }
        $b = { E9 00 00 00 00 60 E8 14 00 00 00 5D 81 ED 00 00 00 00 6A 45 E8 A3 00 00 00 68 00 00 00 00 E8 58 61 EB 39 20 45 78 63 61 6C 69 62 75 72 20 28 63 29 20 62 79 20 66 6F 72 67 6F 74 2F 75 53 2F 44 46 43 47 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 0D 0A 60 9C 9C 6A 63 73 0B EB 02 E8 E8 E8 06 00 00 00 E8 E8 73 F7 E8 E8 83 C4 04 EB 02 E8 E8 FF 0C 24 71 01 E8 79 E0 7A 01 E8 83 C4 04 9D EB 01 E8 E8 01 00 00 00 E9 5D 81 ED AE 28 40 00 9C 6A 63 73 0B EB 02 69 69 E8 06 00 00 00 69 69 73 F7 69 69 83 C4 04 EB 02 69 69 FF 0C 24 71 01 69 79 E0 7A 01 69 83 C4 04 9D EB 01 69 E8 E7 02 00 00 E8 9C 6A 63 73 0B EB 02 69 69 E8 06 00 00 00 69 69 73 F7 69 69 83 C4 04 EB 02 69 69 FF 0C 24 71 01 69 79 E0 7A 01 69 83 C4 04 9D EB 01 69 E8 B4 02 00 00 E8 60 E8 }
    condition:
        for any of ($*) : ( $ 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer runs the eXcalibur binary (or a wrapper script invoking it) locally to test new network scanning features or validate configuration changes before deployment.

  • Filter/Exclusion: Exclude alerts where the process path is located in a known development directory (e.g., C:\Dev\, C:\Projects\, C:\Users\<user>\source\) or where the parent process is a recognized IDE or terminal emulator (e.g., code.exe, pwsh.exe, cmd.exe) and the user account belongs to the Developers or DevOps security group.

• Scenario: An automated scheduled task or CI/CD pipeline agent executes eXcalibur as part of a nightly vulnerability assessment or asset discovery job on a dedicated scan host.

  • Filter/Exclusion: Exclude alerts where the process is launched by a known service account (e.g., svc_scan, ci_agent) or where the parent process is a job scheduler (e.g., Task Scheduler, cron, ansible-playbook) and the host is tagged in CMDB as a “Scan Node” or “Assessment Server.”

• Scenario: A security engineer uses eXcalibur in a controlled lab environment or isolated VM to reproduce a known vulnerability or test detection coverage, often with elevated privileges.

  • Filter/Exclusion: Exclude alerts where the host is identified as a lab or test environment (via hostname suffix like -lab, -test, or -dev) or where the user account is a known security engineering account (e.g., sec_eng_01) and the process is run from a standard tooling directory (e.g., C:\Tools\, C:\SecTools\).

• Scenario: A third-party monitoring or endpoint detection agent bundles