EXEStealthv273

Hunt Hypothesis

This rule identifies potentially stealthy executable files that may be used to establish a foothold or execute malicious payloads, often leveraging obfuscation or packing techniques to evade standard signature-based detection. Proactively hunting for these artifacts in Azure Sentinel allows the SOC team to uncover low-fidelity threats that might slip through initial ingestion filters, ensuring early detection of adversaries attempting to hide their presence within the environment.

YARA Rule

rule EXEStealthv273
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 00 EB 2F 53 68 61 72 65 77 61 72 65 20 2D 20 45 78 65 53 74 65 61 6C 74 68 00 EB 16 77 77 77 2E 77 65 62 74 6F 6F 6C 6D 61 73 74 65 72 2E 63 6F 6D 00 60 90 E8 00 00 00 00 5D 81 ED F0 27 40 00 B9 15 00 00 00 83 C1 05 EB 05 EB FE 83 C7 56 EB 00 83 E9 02 }

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: Execution of legitimate software installers or updaters that bundle compressed executables (e.g., msiexec.exe running a silent install for Adobe Creative Cloud or Java JRE updates). These installers often embed multiple PE headers or use specific compression algorithms that match the EXEStealthv273 signature.

  • Filter/Exclusion: Exclude processes where the parent process is msiexec.exe or setup.exe and the file path contains standard installation directories like \Program Files\ or \AppData\Local\Temp\. Additionally, allow known hashes for major vendor installers (e.g., Adobe, Oracle, Microsoft).

• Scenario: Administrative execution of PowerShell scripts that download and execute temporary binaries for patch management or configuration tasks (e.g., using Start-Process to run a downloaded .exe from C:\Windows\Temp\ or C:\Users\<Admin>\AppData\Local\Temp\). This is common in enterprise automation using tools like SCCM or Ansible.

  • Filter/Exclusion: Exclude executions where the process name is powershell.exe or pwsh.exe and the child process path resides in temporary directories (\Temp\, \Tmp\). Verify that the parent process has a valid digital signature from a trusted vendor (e.g., Microsoft, VMware, Cisco).

• Scenario: Execution of backup or snapshot utilities that create temporary executable wrappers or use in-memory execution for performance (e.g., Veeam Backup & Replication agents, Commvault, or Acronis True Image). These tools often spawn short-lived helper executables that may exhibit stealthy characteristics to avoid file locking issues.

  • Filter/Exclusion: Allow processes spawned by known backup agent services (e.g., VeeamSvc.exe, commvault.exe, `acrsvc.exe