Security1 publisher2 min readPublished
Microsoft confirms its optional KB5124010 preview crashes older apps that use Windows AC-3 decoding
Microsoft confirmed its September 2026 KB5124010 Windows 11 preview crashes some apps that rely on Windows' built-in AC-3 (Dolby Digital) decoding. The update is labelled optional, but 24H2 machines with the early-updates setting switched on install it automatically.
The Watch · Security desk
Drafted by a language model from the sources cited here and checked against its claim ledger before publication. How we use AISend a correction
What happened
- Microsoft says the component behind the crashes is used mostly by legacy apps that still rely on Windows' built-in audio decoding, while modern apps often ship their own AC-3 decoder.
- Games, media players and certain productivity applications are among the software that can be affected, according to Microsoft.
- On machines without the early-updates setting, KB5124010 installs only after a user clicks its "Download and install" link.
- Microsoft is working on a fix but has not estimated when it will arrive, and says it will share more in a future update.
Compiled by The WatchSomething wrong?How this is made
Why it matters
- cost Crashes that wait until a feature such as music playback runs can get past a launch check, so failures tend to surface as user tickets after deployment.
- constraint Until Microsoft names a fix date, keeping the preview off machines with affected software is the only way the record offers to avoid the crash.
- precedent Six audio breakages in about two years, each in a different component, make another audio regression in a future 24H2 update the reasonable expectation.
"In some cases the application can fail to launch, or close without warning. In other cases the application will work normally until certain features are used, such as playing music," Microsoft said in a Friday update to the Windows release health dashboard [4].
For security purposes this one does not matter. Microsoft describes crashes and early exits in audio-dependent software, nothing an attacker can use [1][4]. The cost falls on support staff and on whoever still depends on older software that decodes AC-3 through Windows [6].
On a fleet, the machines that take this update without anyone choosing it are 24H2 devices with "Get the latest updates as soon as they're available" switched on [3]. The ones that break are those running software that leans on Windows' built-in AC-3 decoder [6]. The evidence supports holding KB5124010 on machines that fit both descriptions [3][6]. BleepingComputer's report does not say whether devices under managed update policy pull the preview on their own [3].
Audio has broken repeatedly in Windows servicing. Last month Microsoft shipped emergency updates after its KB5124008 and KB5124012 September security updates caused USB audio problems, along with Remote Desktop Services and Hyper-V failures [8]. In January of last year it fixed audio playback failures and Code 10 errors on 24H2 systems with USB audio drivers [9]. Last year it also lifted a safeguard hold that had blocked upgrades on systems running Dirac audio improvement software, where Bluetooth headsets and speakers malfunctioned [10]. Two years ago it confirmed game audio jumping to full volume on USB DAC setups [11]. In the same period it blocked 24H2 upgrades on machines with incompatible Intel Smart Sound Technology drivers because of blue-screen crashes [12].
Counting KB5124010, BleepingComputer's account lists six audio problems in about two years [1]. They sit in different places: USB audio drivers, Dirac's enhancement software, Intel's SST drivers and now the built-in AC-3 decoder [9][10][12][6].
What to watch
- Microsoft's next release health dashboard update on the AC-3 issue, and whether it includes a fix date or a workaround.
- Whether the AC-3 change reaches 24H2's next monthly security update before a fix does; that would put it on machines that never opted into the preview.
- Any Microsoft statement on whether managed update policies keep 24H2 devices off optional previews like KB5124010.