eXcaliburv103forgotus

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging specific malware signatures identified by the eXcaliburv103forgotus YARA rule to detect early-stage file-based threats that may evade standard signature updates. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to identify low-severity indicators of compromise before they escalate, ensuring comprehensive coverage against emerging variants that might otherwise remain undetected by default rules.

YARA Rule

rule eXcaliburv103forgotus
{
      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 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 }

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

Here are 4 specific false positive scenarios for the eXcaliburv103forgotus YARA rule, along with targeted exclusion strategies:

• Scenario: Automated Password Reset via Active Directory Federation Services (ADFS)

  • Context: The w3wp.exe process hosting ADFS triggers the rule when it executes a scheduled job to reset expired user passwords or sync credential vaults. This often involves memory signatures resembling forgotten password logic.
  • Exclusion Strategy: Add an exclusion for the specific process path and command line arguments:
    • Process Name: w3wp.exe (AppPool: DefaultAppPool)
    • Command Line Filter: Include -app "ADFS" or exclude if the user context is NT SERVICE\W3SVC.

• Scenario: Microsoft Intune Compliance Policy Enforcement

  • Context: The Microsoft.IntuneManagementEngine.exe agent runs nightly compliance checks on endpoints, specifically validating device password age and complexity policies. This activity mimics the “forgotus” signature when the agent interacts with local credential stores.
  • Exclusion Strategy: Create a filter based on the parent process and file hash:
    • Process Name: Microsoft.IntuneManagementEngine.exe
    • Parent Process: MsMpEng.exe (Antivirus) or svchost.exe
    • File Hash Whitelist: Exclude known SHA-256 hashes of the current Intune agent version.

• Scenario: Scheduled Office 365 Credential Sync via Azure AD Connect

  • Context: The AzureADConnect.exe service performs delta synchronization to update user attributes, including password hash changes. When syncing “forgot password” tokens or MFA status updates, the YARA rule may flag the memory dump of these credential objects.