KB5120708 and KB5120710 named in the Windows 11 WPF printing break (August 25, 2026)
Chapters
What is new on August 25
Microsoft's confirmation of the fault is a day old, and I wrote it up in the August 24 post. What changed on August 25, 2026 is the paperwork: which updates, which platforms, and what the workaround actually costs in security terms.
The Register published at 12:27 UTC, written by Richard Speed, and put the fault on the August 11, 2026 .NET Framework cumulative update. PCWorld, written by Hans-Christian Dirscherl, named KB5120708 and described the root cause as a faulty .NET Framework update with a permanent fix still pending. Neither adds a new symptom. Both add the detail an administrator needs to act.
TL;DR
The Windows 11 printing failure in WPF applications got its update numbers on August 25, 2026, when The Register published at 12:27 UTC and traced the fault to the August 11, 2026 .NET Framework cumulative update. PCWorld named KB5120708 in its own write-up on August 25, 2026. The other new fact of the day is the price of Microsoft's only workaround, now stated in full: it "disables security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities addressed by that update".
- The August 25 reports name the updates: KB5120708 for Windows 11 25H2 and the Server OS 24H2 release, KB5120710 for Windows 11 24H2, and KB5120705 for Windows Server 2022.
- The scope is Windows 10, Windows 11 and Windows Server 2012 through Windows Server 2025, which makes this a fleet-wide document-production problem rather than a desktop annoyance.
- Microsoft's own warning about the workaround: it disables the security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities that update addressed.
- Microsoft was still investigating, and no permanent fix had shipped as of August 25, 2026.
- The symptom is unchanged: System.IO.FileFormatException during printing or PDF and XPS export in WPF applications.
The updates, by platform
The August .NET Framework set is not one update. These are the numbers named in the August 25 reporting, mapped to what they install on.
| Update | Platform it applies to |
|---|---|
| KB5120708 | Windows 11 25H2 and the Server OS 24H2 release |
| KB5120710 | Windows 11 24H2 |
| KB5120705 | Windows Server 2022 |
The workaround now has a stated price
The workaround has not changed. It is still the AppContext switch Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection, set in the configuration file of the application that fails.
What is new is that Microsoft's warning is now quoted in full. The switch "disables security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities addressed by that update". Read that as a trade rather than a fix: working printers on one side, the vulnerabilities the August update closed on the other.
Microsoft's guidance is to use it only as a temporary measure and only where it is required. On a server that produces documents unattended, that means setting it on the one process that needs it and putting a date on taking it out again.
Still investigating, still no fix
The Register noted that Microsoft was still investigating both this and the August game-crash issue on Windows 11. PCWorld put it the same way: Microsoft investigating, permanent fix pending.
That matters for planning. As of August 25, 2026 there is no fix build to schedule and no date to hold out for, so the decision in front of anyone running affected apps is whether to accept the workaround's cost now or to leave the printing broken until Microsoft ships something.
What you can do today
The order I would work in on August 25, 2026:
1. Match your platform to the update. KB5120708 on Windows 11 25H2 and the Server OS 24H2 release, KB5120710 on Windows 11 24H2, KB5120705 on Windows Server 2022. Settings > Windows Update > Update history lists what installed this month.
2. List the applications that print or export PDF and XPS from WPF. Servers first: an unattended statement or invoice run fails quietly, while a person at a keyboard tells you straight away.
3. Where a business process is stopped, set the AppContext switch in that application's configuration file and nowhere else.
4. Write the trade into the change record in Microsoft's own words: the switch disables the security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities that update addressed. Whoever approves the change should read that sentence.
5. Set a review date. Microsoft was still investigating as of August 25, 2026, so the switch comes out when a fix ships. A switch with no review date is a permanent hole.
6. Leave the update installed. Removing it takes the August protections off the whole machine, which is a bigger hole than the one the switch opens in a single application.
If you would rather have the affected machines identified and the switch tracked for you, Get XLAnt.
Frequently asked questions
Which update should I look for on my machine?
KB5120708 on Windows 11 25H2 and the Server OS 24H2 release, KB5120710 on Windows 11 24H2, and KB5120705 on Windows Server 2022, as named in the August 25, 2026 reporting. Settings > Windows Update > Update history shows what installed.
Is there a permanent fix yet?
No. As of August 25, 2026 Microsoft was still investigating and the only published remedy was the AppContext switch, which Microsoft describes as temporary because it disables protections the August 2026 update introduced.