EXECryptor2223protectedIAT

Hunt Hypothesis

This rule identifies executable files that have undergone Import Address Table (IAT) protection, a technique often used by malware authors to obscure dependencies and hinder static analysis. Proactively hunting for these artifacts in Azure Sentinel allows the SOC to uncover stealthy binaries that may be evading traditional signature-based detections or preparing for runtime decryption of their import functions.

YARA Rule

rule EXECryptor2223protectedIAT
{
      meta:
		author="malware-lu"
strings:
		$a0 = { CC [3] 00 00 00 00 FF FF FF FF 3C [3] B4 [3] 08 [3] 00 00 00 00 FF FF FF FF E8 [3] 04 [3] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 6B 65 72 6E 65 6C 33 32 2E 64 6C 6C 00 00 00 00 00 00 47 65 74 4D 6F 64 75 6C 65 48 61 6E 64 6C 65 41 00 00 00 00 4C 6F 61 64 4C 69 62 72 61 72 79 41 00 00 00 00 47 65 74 50 72 6F 63 41 64 64 72 65 73 73 00 00 00 00 00 00 45 78 69 74 50 72 6F 63 65 73 73 00 00 00 00 00 56 69 72 74 75 61 6C 41 6C 6C 6F 63 00 00 00 00 56 69 72 74 75 61 6C 46 72 65 65 00 00 00 [24] 4C [3] 60 [3] 70 [3] 84 [3] 94 [3] A4 [3] 00 00 00 00 75 73 65 72 33 32 2E 64 6C 6C 00 00 00 00 4D 65 73 73 61 67 65 42 6F 78 }

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: Antivirus/EDR Engine Updates

  • Description: When enterprise endpoint protection agents (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black) perform background updates or self-healing repairs, they may temporarily write new rule definitions or engine components to disk. These binary files often contain packed or obfuscated sections that match the EXECryptor2223 signature, especially if the update package is compressed or encrypted before deployment.
  • Filter/Exclusion: Exclude file paths containing \CrowdStrike\, \Microsoft\Defender\, or \CarbonBlack\ from the YARA scan scope, or filter by process name falconctl.exe, MsMpEng.exe, or cb.exe when the file is being written.

• Scenario: Software Installer Self-Extraction

  • Description: During the installation of major enterprise applications (e.g., Adobe Creative Cloud, Oracle Java, or SAP GUI), installers often extract temporary executable payloads or license validators to the %TEMP% or %APPDATA% directories. These temporary binaries are frequently packed with custom or commercial packers (like UPX, FSG, or proprietary variants) to reduce size, which can trigger IAT (Import Address Table) protection signatures.
  • Filter/Exclusion: Exclude files located in %TEMP%, %APPDATA%, or %LOCALAPPDATA% that are created by known installer processes such as msiexec.exe, setup.exe, or install.exe. Alternatively, exclude file extensions .tmp or .part if the detection is based on file creation events.

• Scenario: Scheduled Backup or Snapshot Jobs

  • Description: Enterprise backup solutions (e.g., Veeam, Commvault, or Acronis) or disk snapshot utilities may create temporary shadow copies or