detect Bebloh(a.k.a. URLZone) in memory

Hunt Hypothesis

This hunt targets adversaries leveraging the Bebloh (URLZone) browser extension to establish persistent footholds and exfiltrate sensitive data through legitimate web traffic channels within the Azure Sentinel environment. Proactive hunting is essential because this low-severity memory-based indicator often evades traditional signature-only defenses, requiring behavioral analysis to identify subtle compromise patterns before they escalate into significant data breaches.

YARA Rule

rule Bebloh {
          meta:
            description = "detect Bebloh(a.k.a. URLZone) in memory"
            author = "JPCERT/CC Incident Response Group"
            rule_usage = "memory scan"
            reference = "internal research"

          strings:
            $crc32f = { b8 EE 56 0b ca }
            $dga = "qwertyuiopasdfghjklzxcvbnm123945678"
            $post1 = "&vcmd="
            $post2 = "?tver="

          condition: all of them
}

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 4 string patterns in its detection logic.

References

• internal research
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the detect Bebloh (a.k.a. URLZone) in memory rule, tailored for an enterprise environment:

• Endpoint Protection Scanning by CrowdStrike Falcon or SentinelOne

  • Scenario: The EDR agent performs a real-time scan of the URLZone service executable (urlzone.exe) or its associated DLLs. During this process, the scanner injects memory hooks or loads the module into memory to analyze behavior, triggering the detection logic even though no malicious activity is occurring.
  • Filter/Exclusion: Exclude alerts where the parent process is the EDR service (e.g., csfalcon.exe, SentinelOneService.exe) and the event type indicates “File Scan” or “Memory Injection.”

• Scheduled Group Policy Object (GPO) Deployment

  • Scenario: A scheduled GPO task runs during off-hours to deploy or update security policies related to network zones. This task invokes urlzone.exe to refresh zone configurations on client machines, causing the process to load into memory and execute standard administrative functions that mimic the rule’s detection criteria.
  • Filter/Exclusion: Create an exclusion for events occurring between 02:00 and 05:00 UTC where the initiating user is a known service account (e.g., DOMAIN\GPO_Svc_Account) or the command line arguments contain standard GPO flags like /update or /refresh.

• Microsoft Office Click-to-Run Updates

  • Scenario: The Microsoft Office Click-to-Run update mechanism frequently interacts with URL zone configurations to manage download permissions for add-ins and templates. When OfficeC2RClient.exe triggers a background update, it may spawn or interact with urlzone.exe, resulting in legitimate memory footprint detection that resembles the Bebloh signature.