New Windows Defender zero-day blocks Microsoft antivirus updates

Key Takeaways

• A new Windows Defender zero-day has been discovered that blocks Microsoft antivirus updates, effectively disabling critical security coverage on affected Windows systems.
• The vulnerability weaponizes Windows Defender itself to prevent security updates, creating a catch-22 where the security tool becomes the vector for maintaining an unpatched state.
• Windows administrators should verify that Defender definitions and engine updates are installing correctly and apply workarounds if the update blocking behavior is observed.