Microsoft ships Windows 10 KB5099539 as record 570-flaw Patch Tuesday lands

Key points

• Microsoft released the Windows 10 KB5099539 update on July 14, 2026, part of a Patch Tuesday fixing 570 vulnerabilities.
• The July 2026 batch includes two flaws already being exploited by attackers and one publicly disclosed zero-day.
• Microsoft extended its free Extended Security Updates programme for home users, giving enrolled Windows 10 devices patches until October 12, 2027.
• After installing, Windows 10 moves to build 19045.7548 and Windows 10 Enterprise LTSC 2021 to build 19044.7548.
• A new networking change may break older apps that rely on unregistered third-party TDI transports.

Microsoft has released a big Windows 10 security update, KB5099539, alongside a July 2026 Patch Tuesday that fixes a record 570 vulnerabilities across its products.

A vulnerability is a flaw in software that attackers can abuse to break in, steal data, or take control of a machine. Patch Tuesday is Microsoft's monthly release day for security fixes, always the second Tuesday.

Three of the flaws patched this month are what the industry calls zero-days: bugs that were being used or publicly known before Microsoft had a fix ready. Two are already being exploited in real attacks. The third had been disclosed openly.

Do I still get updates if I'm on Windows 10?

Yes, for now. Microsoft officially ended free support for Windows 10 last year, but it has quietly extended its Extended Security Updates programme for home users by another twelve months. Enrolled devices will keep receiving security patches until October 12, 2027.

That matters because hundreds of millions of PCs still run Windows 10. Without patches, each new flaw becomes a permanent open door.

If you are on Windows 10 Enterprise LTSC or signed up to the ESU programme, the update arrives through the normal route: open Settings, click Windows Update, and hit Check for Updates. After it installs, your build number will read 19045.7548, or 19044.7548 on Enterprise LTSC 2021.

What is actually in this update?

Microsoft is no longer adding new features to Windows 10, so KB5099539 is almost entirely security fixes and bug repairs, as first reported by BleepingComputer.

The smaller fixes tidy up problems introduced by June's update. One issue broke certain older applications that use a Windows component called OLE Automation to talk between programs. Another caused the OneDrive shortcut in File Explorer to stop working when File Explorer was run as an administrator. A third made the Recycle Bin show an internal file name, rather than the original name, when you permanently deleted a file.

There is also a change to Secure Boot, the feature that stops tampered software loading when your PC starts. Windows Security will now show a live status for Secure Boot, and Microsoft is widening the rollout of new Secure Boot certificates to more machines.

Remote Desktop, the tool that lets people log into a PC from elsewhere, gets a security tightening. Microsoft is moving away from an old signing method called SHA-1 to the stronger SHA-256. IT administrators are being told to switch as soon as possible.

Should I be worried about anything breaking?

Mostly no, but there is one catch worth flagging.

Microsoft has hardened a piece of networking plumbing called TDI. In plain terms: some very old third-party networking add-ons that never properly registered themselves with Windows will stop working after this update. Modern apps are unaffected.

If a business app suddenly loses network access after patching, an administrator can check the Windows Event Viewer for an entry marked AFD Event ID 16003. That message names the offending driver.

For ordinary home users, there is nothing to do beyond installing the update. Two of the fixed flaws are being exploited right now, which means delaying is the risky option. Turn the machine on, let Windows Update run, and reboot when it asks.