This detection identifies potential file encryption activities associated with the SimpleUPX cryptor, which adversaries often leverage to obfuscate malware payloads and evade static analysis. Proactively hunting for this behavior in Azure Sentinel is essential to uncover early-stage intrusion attempts where attackers utilize single-layer encryption to conceal malicious executables before they execute their primary attack logic.
rule SimpleUPXCryptorv3042005OnelayerencryptionMANtiCORE
{
meta:
author="malware-lu"
strings:
$a0 = { 60 B8 [3] 00 B9 ?? 01 00 00 80 34 08 ?? E2 FA 61 68 [3] 00 C3 }
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.
Here are 4 specific false positive scenarios for the SimpleUPXCryptorv3042005OnelayerencryptionMANtiCORE rule, including suggested filters and exclusions:
Scenario: Scheduled Backup of UWP Application Data
C:\Users\Public\AppData\Packages. These backup processes often package application data into .upx compressed archives before encryption, triggering the rule’s detection of “one-layer encryption” on UWP-like structures.VeeamAgent.exe, AcronisCyberProtectService.exe, or TaskScheduler.exe (specifically when the command line contains backup keywords like /backup or -archive).Scenario: Deployment of UWP Apps via Intune
.appx or .msix bundles which utilize UPX compression internally. The YARA rule may flag the extraction process as a cryptor activity due to the internal encryption layer of the package manifest.C:\Program Files\Microsoft Intune Agent or C:\Windows\System32\smss.exe when the target file extension is .appx, .msix, or .cab.Scenario: Antivirus Real-Time Scanning of Compressed Archives