AppEncryptorSilentTeam

Hunt Hypothesis

This rule detects the presence of the AppEncryptorSilentTeam YARA signature, which likely indicates the deployment of a specific encryption or obfuscation tool used by adversaries to hide malicious payloads or encrypt data during post-compromise activities. Proactively hunting for this indicator allows the SOC team to identify low-severity, stealthy tooling that may precede data exfiltration or ransomware execution before it escalates into a higher-impact incident.

YARA Rule

rule AppEncryptorSilentTeam
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 81 ED 1F 1F 40 00 B9 7B 09 00 00 8D BD 67 1F 40 00 8B F7 AC }

condition:
		$a0 at pe.entry_point
}

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

• Legitimate Application Deployment via Group Policy or SCCM

  • Scenario: Enterprise IT teams deploy proprietary line-of-business applications (e.g., custom ERP clients or internal dashboards) using System Center Configuration Manager (SCCM) or Group Policy Objects (GPO). These installers often use silent flags (/S, /quiet) and may be signed by internal CA or third-party vendors that match the AppEncryptorSilentTeam YARA signature due to shared obfuscation techniques or specific PE header structures.
  • Filter/Exclusion: Exclude processes where the parent process is ccmsetup.exe, wuaexehost.exe, or gpupdate.exe, and the file path resides under standard deployment directories such as C:\Windows\CCM\ or C:\ProgramData\Microsoft\CCM\.

• Third-Party Endpoint Security Agent Updates

  • Scenario: Security vendors like CrowdStrike, Carbon Black, or SentinelOne perform background updates or component installations. These updates often run as silent services or scheduled tasks and may utilize encryption/obfuscation layers that trigger the YARA rule, especially if the vendor’s update binary shares structural similarities with the targeted AppEncryptorSilentTeam family.
  • Filter/Exclusion: Exclude processes signed by known security vendor certificates (e.g., CrowdStrike, Inc., Palo Alto Networks, Inc.) or where the executable name matches known agent binaries (e.g., FalconSensor.exe, cb.exe, sentineloneagent.exe).

• Scheduled Maintenance Jobs for Backup Software

  • Scenario: Backup solutions like Veeam, Acronis, or Commvault run scheduled maintenance or license renewal tasks. These jobs often execute silent installers or configuration scripts that encrypt payloads or use specific compression/encryption algorithms, potentially matching