New BigDiskBuster zero-day blocks Microsoft Defender updates

Security researcher Abdelhamid Naceri released a new Microsoft Defender zero-day exploit called BigDiskBuster that blocks antivirus platform and signature updates when running in the background. He says it works on all supported Windows versions and is similar to the UnDefend flaw he released in April.

• BigDiskBuster blocks Defender platform and signature updates
• Works on all supported Windows versions, needs background execution
• Similar to UnDefend, released in April 2026
• Naceri has released nearly a dozen zero-days since April 2026