kkrunchy023alphaRyd

Hunt Hypothesis

This hunt hypothesis targets the presence of a specific malware signature identified by the “kkcrunchy023alphaRyd” YARA rule to detect potential file-based threats within the environment. The SOC team should proactively hunt for this indicator in Azure Sentinel to validate its relevance and uncover any associated low-severity incidents that may indicate early-stage adversary activity before escalation.

YARA Rule

rule kkrunchy023alphaRyd
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BD 08 [2] 00 C7 45 00 [3] 00 FF 4D 08 C6 45 0C 05 8D 7D 14 31 C0 B4 04 89 C1 F3 AB BF [3] 00 57 BE [3] 00 31 C9 41 FF 4D 0C 8D 9C 8D A0 00 00 00 FF D6 10 C9 73 F3 FF 45 0C 91 AA 83 C9 FF 8D 5C 8D 18 FF D6 74 DD E3 17 8D 5D 1C FF D6 74 10 8D 9D A0 08 00 00 E8 ?? 00 00 00 8B 45 10 EB 42 8D 9D A0 04 00 00 E8 ?? 00 00 00 49 49 78 40 8D 5D 20 74 03 83 C3 40 31 D2 42 E8 ?? 00 00 00 8D 0C 48 F6 C2 10 74 F3 41 91 8D 9D A0 08 00 00 E8 ?? 00 00 00 3D 00 08 00 00 83 D9 FF 83 F8 60 83 D9 FF 89 45 10 56 89 FE 29 C6 F3 A4 5E EB 90 BE [3] 00 BB [3] 00 55 46 AD 85 C0 74 ?? 97 56 FF 13 85 C0 74 16 95 AC 84 C0 75 FB 38 06 74 E8 78 ?? 56 55 FF 53 04 AB 85 C0 }

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 kkrunchy023alphaRyd YARA rule, tailored to a legitimate enterprise environment:

• Scenario: Legitimate deployment of Microsoft Office 365 Click-to-Run updates where the update engine (OfficeClickToRun.exe) extracts temporary installer payloads containing embedded scripts that match the rule’s signature for “embedded executable extraction.”

  • Suggested Filter/Exclusion: Exclude processes with ImageName matching *OfficeClickToRun.exe and CommandLine containing /update or /install, specifically within the C:\Program Files\Microsoft Office root directory.

• Scenario: Scheduled nightly backup jobs executed by Veeam Backup & Replication which spawn temporary worker processes (vrbkworker.exe) to compress and archive data, triggering the rule due to the presence of compressed archives with embedded metadata resembling the detection logic.

  • Suggested Filter/Exclusion: Create a whitelist for ImageName equal to vrbkworker.exe running under the service account NT SERVICE\VeeamBackupService, and exclude events occurring during the defined maintenance window (e.g., 01:00–04:00 UTC).

• Scenario: Execution of CrowdStrike Falcon or SentinelOne endpoint protection agents performing real-time heuristic scanning, where their internal engine generates temporary sandboxed artifacts that mimic the “suspicious memory injection” pattern defined in kkrunchy023alphaRyd.

  • Suggested Filter/Exclusion: Apply a filter to exclude alerts generated by parent processes with ImageName containing FalconSensor.exe, SentinelOneAgent.exe, or csagent.exe, provided the child process is running within the vendor’s installation directory (e.g., `C:\Program Files\C