RSCsProcessPatcherv14

Hunt Hypothesis

This hypothesis targets adversaries who employ process patching techniques to modify in-memory code execution, a behavior often used to bypass security controls or hide malicious logic within legitimate processes. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to identify subtle memory manipulations that may evade traditional signature-based detections, ensuring early visibility into stealthy post-exploitation activities.

YARA Rule

rule RSCsProcessPatcherv14
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 E1 01 00 00 80 38 22 75 13 80 38 00 74 2E 80 38 20 75 06 80 78 FF 22 74 18 40 EB ED 80 38 00 74 1B EB 19 40 80 78 FF 20 75 F9 80 38 00 74 0D EB 0B 40 80 38 00 74 05 80 38 22 74 00 8B F8 B8 04 60 40 00 68 00 20 40 00 C7 05 A2 20 40 00 44 00 00 00 68 92 }

condition:
		$a0
}

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 DevOps team uses Ansible or Puppet to deploy configuration patches to a fleet of Windows servers, where the agent process (e.g., ansible-service-runner.exe or puppet-agent.exe) temporarily hooks into target processes to apply file or registry changes.

  • Filter/Exclusion: Exclude processes where the parent process name is ansible-service-runner.exe, puppet-agent.exe, or chef-client.exe and the working directory is within the standard agent installation path (e.g., C:\ProgramData\ansible\ or C:\Program Files\Puppet\).

• Scenario: An IT administrator runs Sysinternals Process Monitor (procmon.exe) or Process Explorer (procexp.exe) to debug application performance, which involves attaching to and inspecting process memory structures that may mimic patching behavior in YARA signatures.

  • Filter/Exclusion: Exclude processes where the image path matches C:\Tools\Sysinternals\procmon.exe or C:\Tools\Sysinternals\procexp.exe and the user context is an interactive admin session (e.g., Domain\ITAdmin*).

• Scenario: A scheduled task for Windows Update or WSUS client service (wuauclt.exe or usocsvc.exe) performs in-place patching of system binaries, which can trigger memory patching heuristics if the YARA rule inspects loaded modules.

  • Filter/Exclusion: Exclude processes where the image name is wuauclt.exe or usocsvc.exe and the command line contains arguments related to detection or reporting (e.g., /detectnow or /reportnow).

• Scenario: A security team deploys CrowdStrike Falcon or Carbon Black agents, which use in