WebCopsEXELINKDataSecurity

Hunt Hypothesis

This detection identifies potential data exfiltration or malicious document interactions by analyzing Excel files containing external web links that match specific security signatures defined in the WebCops YARA rule. A proactive hunt is essential to uncover stealthy adversaries leveraging benign office documents as a vector for lateral movement or initial access, ensuring early identification of compromised assets within the Azure Sentinel environment before broader impact occurs.

YARA Rule

rule WebCopsEXELINKDataSecurity
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 03 05 EB 02 EB FC 55 EB 03 EB 04 05 EB FB EB 53 E8 04 00 00 00 72 }

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 WebCopsEXELINKDataSecurity detection rule, including suggested filters and exclusions:

• Scenario: Scheduled Macro Execution in Finance Reports

  • Context: The nightly finance consolidation job uses a PowerShell script to open Excel files containing embedded hyperlinks (<a href="...">) that point to internal PowerBI dashboards or external vendor portals. The YARA rule flags these as potential data exfiltration attempts via web links within Office documents.
  • Filter/Exclusion: Create an exclusion for the specific service account running the job (e.g., DOMAIN\svc-finance-etl) and restrict the detection to exclude file paths under \\Finance-Share\Reports\MonthlyConsolidation\. Additionally, add a filter to ignore links pointing to trusted internal domains (e.g., *.internal.corp, *.powerbi.com).

• Scenario: Admin Deployment of Standardized Templates via SCCM

  • Context: During monthly software updates, the Systems Management team uses Microsoft Endpoint Configuration Manager (SCCM) to push a standardized Excel template containing pre-configured hyperlinks to HR policy documents. The rule triggers because the deployment agent modifies these files on user endpoints, interpreting the link metadata as active data movement.
  • Filter/Exclusion: Exclude processes initiated by ccmexec.exe and wuauserv.exe. Furthermore, add a hash-based exclusion for the specific SHA-256 hash of the standardized template file (Template_HR_Policy_v4.xlsx) to prevent repeated alerts on identical files.

• Scenario: Automated Compliance Audit Scans by Qualys

  • Context: The Qualys Cloud Agent performs weekly vulnerability scans that involve parsing active Excel workbooks in shared network folders to verify link integrity and access controls. This scanning activity mimics the behavior