Microsoft's August 2026 security update patches 400 vulnerabilities, including active zero-days

Microsoft releases its August 2026 security update, addressing around 400 vulnerabilities including three zero-days, one actively exploited and posing significant risks across Windows systems, alongside quality enhancements in Windows 11.

Microsoft has released its August 2026 security update with a broad sweep of fixes across Windows and related components, addressing about 400 vulnerabilities in total. Among them are 42 rated Critical, the majority of which are remote code execution flaws, while others can be used to raise privileges. The release also includes three zero-day issues, one of which was already being exploited in the wild, according to WindowsReport and security researchers cited in its coverage.

The most serious actively abused flaw is CVE-2026-68820 in the Windows Ancillary Function Driver for WinSock. Microsoft says the use-after-free bug could let a locally authenticated attacker gain SYSTEM-level rights by running a crafted application that triggers a race condition. The company has not disclosed how the vulnerability was used in real-world attacks. Microsoft also patched CVE-2026-62832, a publicly disclosed privilege-escalation issue in the Windows User Profile Service that appears to correspond to the previously discussed LegacyHive bug. In practical terms, an attacker with access to another local account could load that user’s registry hive, potentially reading or changing data and, in some cases, reaching administrator access.

A third zero-day, CVE-2026-72971, affects the Windows Container Isolation FS Filter Driver, unionfs.sys. Microsoft describes it as a tampering flaw tied to improper link resolution, which could be used by a locally authenticated attacker. Alongside those fixes, the August release covers 176 elevation-of-privilege issues, 110 remote code execution vulnerabilities, 86 information disclosure bugs, 21 spoofing flaws, 12 denial-of-service issues and 11 security feature bypass problems. Those figures cover the vulnerabilities patched in this month’s Patch Tuesday cycle and do not include other Microsoft security fixes delivered earlier in August.

The update also arrives as Microsoft continues to ship broader monthly changes to Windows 11. Windows Central reported that the August package adds refinements such as support for external fingerprint sensors in Windows Hello Enhanced Sign-in Security, the option to remove the Image Generation AI model and several usability tweaks in Search, File Explorer and power settings. Windows 11 users received cumulative updates KB5121003 and KB5120240, while Windows 10 devices enrolled in Extended Security Updates received KB5120249. The pattern follows several recent Patch Tuesday releases that have grown unusually large, which security writers have linked to Microsoft’s expanded use of AI-assisted vulnerability discovery.