Themida10xx18xxnocompressionOreansTechnologies

Hunt Hypothesis

This hypothesis targets the presence of binaries packed with the Themida protector, a technique frequently employed by adversaries to obscure executable code and evade static analysis during initial access or persistence phases. Proactively hunting for these signatures in Azure Sentinel allows the SOC to identify potentially obfuscated payloads within workloads or endpoints before they can execute complex logic or deploy additional malware.

YARA Rule

rule Themida10xx18xxnocompressionOreansTechnologies
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 D8 60 E8 00 00 00 00 5A 81 EA [4] 8B DA C7 45 D8 00 00 00 00 8B 45 D8 40 89 45 D8 81 7D D8 80 00 00 00 74 0F 8B 45 08 89 83 [4] FF 45 08 43 EB E1 89 45 DC 61 8B 45 DC C9 C2 04 00 55 8B EC 81 C4 7C FF FF FF 60 E8 00 00 00 00 }
	$a1 = { 55 8B EC 83 C4 D8 60 E8 00 00 00 00 5A 81 EA [4] 8B DA C7 45 D8 00 00 00 00 8B 45 D8 40 89 45 D8 81 7D D8 80 00 00 00 74 0F 8B 45 08 89 83 [4] FF 45 08 43 EB E1 89 45 DC 61 8B 45 DC C9 C2 04 00 55 8B EC 81 C4 7C FF FF FF 60 E8 00 00 00 00 5A 81 EA [4] 8D 45 80 8B 5D 08 C7 85 7C FF FF FF 00 00 00 00 8B 8D 7C FF FF FF D1 C3 88 18 41 89 8D 7C FF FF FF 81 BD 7C FF FF FF 80 00 00 00 75 E3 C7 85 7C FF FF FF 00 00 00 00 8D BA [4] 8D 75 80 8A 0E BB F4 01 00 00 B8 AB 37 54 78 D3 D0 8A 0F D3 D0 4B 75 F7 0F AF C3 47 46 8B 8D 7C FF FF FF 41 89 8D 7C FF FF FF 81 F9 80 00 00 00 75 D1 61 C9 C2 04 00 55 8B EC 83 C4 F0 8B 75 08 C7 45 FC 00 00 00 00 EB 04 FF 45 FC 46 80 3E 00 75 F7 BA 00 00 00 00 8B 75 08 8B 7D 0C EB 7F C7 45 F8 00 00 00 00 EB }

condition:
		$a0 or $a1
}

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

• Scenario: A developer or DevOps engineer runs a custom .NET application or C# executable that has been protected with Themida v10.x (specifically build 18xx) using the “No Compression” option to optimize startup time for a critical internal service.

  • Filter/Exclusion: Exclude files located in specific development or staging directories (e.g., C:\Dev\Projects\*, C:\Temp\Builds\*) or exclude processes where the parent is a known IDE or build tool (e.g., dotnet.exe, msbuild.exe, visualstudio.exe).

• Scenario: An IT administrator deploys a patched version of a legacy line-of-business application (e.g., a custom inventory management tool) that was re-protected with Themida 10.18.00 to fix a vulnerability, and the new binary is copied to the standard application directory on user workstations.

  • Filter/Exclusion: Exclude binaries matching the specific version string in the file metadata (e.g., FileVersion: 10.18.*) or exclude files in the standard application install path (e.g., C:\Program Files\InternalApps\*) if the application is whitelisted in the asset inventory.

• Scenario: A scheduled PowerShell script or task runs a small utility tool (e.g., a log rotation script or a data migration helper) that was compiled and protected with Themida 10.18.00 without compression to reduce file size for easier distribution via network shares.

  • Filter/Exclusion: Exclude processes where the command line contains specific keywords associated with the utility (e.g., rotate, migrate, cleanup) or exclude files located in the scheduled tasks’ working directory (e.g., C:\Scripts\Jobs\*).