This rule identifies potentially obfuscated or packed executable files that may be used by adversaries to hide malicious code from static analysis tools. Proactively hunting for these artifacts in Azure Sentinel helps detect early-stage fileless or low-fidelity malware deployments that might otherwise slip past standard signature-based detections.
rule ExeShieldv17
{
meta:
author="malware-lu"
strings:
$a0 = { EB 06 68 90 1F 06 00 C3 9C 60 E8 02 00 00 00 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB 3F 90 }
condition:
$a0 at pe.entry_point
}This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
Scenario: A developer or system administrator uses a legitimate binary packing tool like UPX to compress a custom utility or script to reduce its disk footprint before deployment. The YARA rule ExeShieldv17 likely targets specific byte patterns or section headers associated with packed executables, causing the compressed binary to match the signature.
C:\Dev\, D:\Builds\) or add an exclusion for binaries where the UPX section is present and the file size is below a certain threshold (e.g., < 5MB), provided the parent process is a known compiler or build tool (e.g., msbuild.exe, dotnet.exe).Scenario: An enterprise endpoint protection agent (such as CrowdStrike Falcon, Carbon Black, or Trellix) performs a self-update or integrity check by temporarily writing a packed or obfuscated helper executable to a temporary directory to verify its own hash or perform a quick scan. The rule may flag this transient, packed helper binary as suspicious.
C:\ProgramData\CrowdStrike\, C:\Windows\Temp\CB\) where the parent process is the known EDR agent service (e.g., FalconSensor.exe, CbService.exe).Scenario: A scheduled maintenance job runs a legitimate backup or archival utility like Veeam Backup & Replication or Acronis True Image that uses a packed installer or helper module to initialize the backup engine. These installers often use standard packing techniques to reduce download size, triggering the ExeShieldv17 rule when the temporary executable is extracted and executed.