Microsoft released the October 14, 2025 cumulative update KB5066791 for Windows 10, and it patches several zero-day vulnerabilities that have been exploitable before fixes were available. For most people still running Windows 10, this is the last free security fix of that kind.
The update, listed on Microsoft’s KB page for KB5066791, includes fixes for a group of critical issues. Microsoft’s security guidance, as outlined in its security update guide, indicates that the patched problems range from privilege escalation to secure boot bypass, memory corruption, and exposure of TPM information.
Users who keep Windows Update enabled should receive KB5066791 automatically. After this cumulative update and the other fixes bundled in it are applied, Windows 10 will no longer get the same level of free security updates. Microsoft says customers can continue receiving updates through its paid Extended Security Updates program, though that option is limited to specific devices and regions and carries a cost. The program and details are explained on Microsoft’s end-of-support page for Windows 10 at Microsoft’s end-of-support hub. Bleeping Computer also covered the rollout and its timing relative to the end of support in its own report at Bleeping Computer.
Patch Notes – KB5066791
- Fix for privilege escalation vulnerabilities.
- Patch for secure boot bypass issues.
- Memory corruption flaws addressed.
- Mitigations for TPM information disclosure.
Zero-day bugs are serious because attackers can exploit them before a patch exists. With Windows 10 leaving mainstream updates behind, the practical advice is simple: install KB5066791 when it appears on your machine, consider moving to a supported release, or evaluate whether your device qualifies for Extended Security Updates.
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