Thinstall3035Jtit

Hunt Hypothesis

This detection identifies potential software installation activities captured by the Thinstall3035Jtit YARA signature, which may indicate an adversary establishing persistence or deploying tools within the environment. A proactive hunt is essential to validate these installations against known baselines and uncover stealthy execution patterns that could serve as early indicators of a broader compromise in Azure Sentinel.

YARA Rule

rule Thinstall3035Jtit
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 68 53 74 41 6C 68 54 68 49 6E E8 00 00 00 00 58 BB 37 1F 00 00 2B C3 50 68 [4] 68 00 28 00 00 68 04 01 00 00 E8 BA FE FF FF E9 90 FF FF FF CC CC CC CC CC CC CC 55 8B EC 83 C4 F4 FC 53 57 56 8B 75 08 8B 7D 0C C7 45 FC 08 00 00 00 33 DB BA 00 }
	$a1 = { 9C 60 68 53 74 41 6C 68 54 68 49 6E E8 00 00 00 00 58 BB 37 1F 00 00 2B C3 50 68 [4] 68 00 28 00 00 68 04 01 00 00 E8 BA FE FF FF E9 90 FF FF FF CC CC CC CC CC CC CC 55 8B EC 83 C4 F4 FC 53 57 56 8B 75 08 8B 7D 0C C7 45 FC 08 00 00 00 33 DB BA 00 00 00 80 43 33 C0 E8 19 01 00 00 73 0E 8B 4D F8 E8 27 01 00 00 02 45 F7 AA EB E9 E8 04 01 00 00 0F 82 96 00 00 00 E8 F9 00 00 00 73 5B B9 04 00 00 00 E8 05 01 00 00 48 74 DE 0F 89 C6 00 00 00 E8 DF 00 00 00 73 1B 55 BD 00 01 00 00 E8 DF 00 00 00 88 07 47 4D 75 F5 E8 C7 00 00 00 72 E9 5D EB A2 B9 01 00 00 00 E8 D0 00 00 00 83 C0 07 89 45 F8 C6 45 F7 00 83 F8 08 74 89 E8 B1 00 00 00 88 45 F7 E9 7C FF FF FF B9 07 00 00 00 E8 AA 00 00 00 50 33 C9 B1 02 E8 A0 00 00 00 8B C8 41 41 58 0B C0 74 04 8B D8 EB 5E 83 F9 02 74 6A 41 E8 88 00 00 00 89 45 FC E9 48 FF FF FF E8 87 00 00 00 49 E2 09 8B C3 E8 7D 00 00 00 EB 3A 49 8B C1 55 8B 4D FC 8B E8 33 C0 D3 E5 E8 5D 00 00 00 0B C5 5D 8B D8 E8 5F 00 00 00 3D 00 00 01 00 73 14 3D FF 37 00 00 73 0E 3D 7F 02 00 00 73 08 83 F8 7F 77 04 41 41 41 41 56 8B F7 2B F0 F3 A4 5E E9 F0 FE FF FF 33 C0 EB 05 8B C7 2B 45 0C 5E 5F 5B C9 C2 08 00 03 D2 75 08 8B 16 83 C6 04 F9 13 D2 C3 B9 08 00 00 00 E8 01 00 00 00 C3 33 C0 E8 E1 FF FF FF 13 C0 E2 F7 C3 33 C9 41 E8 D4 FF FF FF 13 C9 E8 CD FF FF FF 72 F2 C3 }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Thinstall3035Jtit detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Updates

  • Context: The Office Click-to-Run (C2R) service (OfficeClickToRun.exe) frequently executes installation logic that matches the YARA signature when updating or repairing Office suites. This often occurs during business hours via scheduled tasks triggered by MsUpdate or user-initiated repairs.
  • Filter/Exclusion: Exclude processes where the parent process is SoftwareProtectionPlatform.exe (Office Protection Service) and the file path contains \Microsoft Office ClickToRun\. Additionally, filter out events occurring within the standard maintenance window (e.g., 02:00–04:00 local time).

• Scenario: Endpoint Antivirus Definition Updates

  • Context: Major EDR/Anti-malware solutions like CrowdStrike (csfalcon.exe), Microsoft Defender (MsMpEng.exe), or SentinelOne (SentinelOneAgent.exe) perform frequent definition and engine updates that involve installing new components. These installation activities often trigger the Thinstall3035Jtit rule due to similar binary structures.
  • Filter/Exclusion: Create a whitelist for known EDR executables. Specifically, exclude any event where the ProcessName matches csfalcon.exe, MsMpEng.exe, or SentinelOneAgent.exe and the command line arguments contain keywords like “update”, “install”, or “definition”.

• Scenario: Patch Management Tool Execution (e.g., SCCM/Intune)

  • Context: Enterprise patch management tools such as Microsoft Endpoint Configuration Manager (SCCM) or Intune utilize ccmsetup.exe or `IntuneManagementExtension.exe