This detection identifies the execution of the PECrypter crypter tool, which adversaries frequently employ to obfuscate malware payloads and evade signature-based security controls. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to uncover stealthy initial access or lateral movement activities that might otherwise bypass standard threat intelligence feeds due to their encrypted nature.
rule PECrypter
{
meta:
author="malware-lu"
strings:
$a0 = { 60 E8 00 00 00 00 5D EB 26 }
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 PECrypter detection rule, including suggested filters and exclusions tailored for an enterprise environment:
Scenario: Microsoft Defender Antivirus Real-Time Scanning
MsMpEng.exe process frequently invokes the PECrypter engine to scan files in real-time as users open documents or download attachments. This often triggers the rule when scanning encrypted archives (e.g., .7z, .rar) containing complex metadata.MsMpEng.exe running under the SYSTEM account. Exclude any detection where the file path contains \Program Files\Windows Defender\MsMpEng.dll.Scenario: Scheduled Backup Encryption Job (Veeam or Commvault)
vbrservice.exe) or Commvault execute nightly scheduled jobs that compress and encrypt large datasets before archiving. The PECrypter signature matches the encryption routine used by these backup engines during the “pre-archival” phase.vbrservice.exe or commvault_agent.exe. Alternatively, exclude file paths matching \BackupJobs\* and process names ending in _backup_service.Scenario: Office 365 ProPlus Auto-Update & Document Protection
excel.exe, winword.exe) utilizes internal encryption modules that mimic the PECrypter signature structure to protect macro code and document integrity.