Microsoft Defender Antivirus security intelligence Sept. 2025

[harlan4096]

September-2025 (Platform: 4.18.25090.3009 | Engine: 1.1.25090.3001)

• Security intelligence update version: 1.439.345.0
  
• Release date: September 8, 2025 (Engine) / September 21, 2025 (Platform)
  
• Platform: 4.18.25090.3009
  
• Engine: 1.1.25090.3001
  
• Support phase: Security and Critical Updates
  

 What's new​ 

• Improved service startup behavior: The core service now only restarts when necessary, for example, during a successful platform update. This change allows the organization to avoid unnecessary restarts when the service is already running correctly.
  
• Improved stability for RPC services: Added input validation across multiple RPC endpoints to prevent crashes caused by malformed data, which addresses a reported security vulnerability.
  
• Fixed threat exclusion handling: Resolved an issue where severity-based exclusions could cause the engine to misidentify threats, potentially skipping high severity detections.
  
• Restored performance optimization for network file access: Fixed a regression that caused slowdowns during file operations, like robocopy to network shares. The fix included reintroducing the logic to skip unnecessary checks on non-local files when Controlled Folder Access is enabled.