kkrunchyRyd

Hunt Hypothesis

This YARA rule targets specific memory patterns associated with the kkrunchyRyd signature, potentially indicating the presence of a low-severity malware implant or custom script used for initial access or persistence. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify stealthy, low-noise threats that may evade standard behavioral detections and establish a foothold before escalating privileges.

YARA Rule

rule kkrunchyRyd
{
      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 }

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

• Scenario: A developer or DevOps engineer uses kkrunchyRyd (a known YARA rule often associated with detecting specific memory patterns or obfuscated code) to scan a local build artifact or a container image layer during a CI/CD pipeline validation step. The rule may match benign binary structures in compiled Go or Rust binaries that resemble the pattern.

  • Filter/Exclusion: Exclude processes originating from CI/CD agent binaries (e.g., jenkins-agent, drone-runner, github-actions-runner) or files located in standard build directories (e.g., /builds/, /artifacts/, C:\Jenkins\workspace\).

• Scenario: An enterprise endpoint detection tool (such as CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black) loads the kkrunchyRyd YARA rule into its in-memory scanning engine to monitor for specific threat signatures. The rule itself exists in the memory of the security agent process, triggering a self-match or a match against the agent’s own memory space.

  • Filter/Exclusion: Exclude matches where the parent process is a known EDR/AV agent (e.g., FalconSensor.exe, MsMpEng.exe, cb.exe) or where the memory region belongs to a known security tool executable.

• Scenario: A database administrator runs a custom performance tuning script or a memory dump analysis tool (like WinDbg or Volatility) that loads YARA rules to inspect heap allocations or specific data structures in a database server process (e.g., sqlservr.exe, postgres). The rule may match legitimate memory layouts used by the database engine for caching or indexing.

  • Filter/Exclusion: Exclude matches in processes associated with major database engines (e.g., sqlservr.exe, mysqld.exe, postgres, `oracle