The short version is: some of them. Software, OS, and generally tech blogs are so fucking lazy now. This is not the first time IT pros have seen this driver act up; it’s been causing problems for like a decade. Here’s what is actually happening with Windows Update KB5121003.
You’ve probably seen it around Bluesky a good bit already; there are a bunch of posts going on indicating that Windows Update KB5121003 is causing massive crash and performance issues in games and intensive apps, and that’s true – that does not seem to be misinformation. However, I want to explain it in a lot more detail right now, since it’s a problem that’s been happening long before now and rears its ugly head every couple of years or so. Not only that, you can see if you’re susceptible to this ahead of time or even after the fact, and it’s a generally easy problem to fix in probably 99% of use cases if you’re a typical end user. So! Instead of having to sensationalize the issue for clicks, let’s talk about actually why this is going on.
The likely culprit: inpoutx64.sys
The current offender, if the theory holds at this time, is not something that came installed with this Windows Update. Instead, it’s something that is inexplicably installed on a lot of OEM Windows configurations already (or installed through innocuous driver packages for other niche hardware, such as Tobii Eye Tracker) and just generally lays unused and dormant. Stranger yet, the original purpose of this driver was to interface with LPT ports, a type of port that was most common in the DOS and very early Windows days of computing. So why in the world is this driver causing problems to this day?
Well it turns out no matter how you got it to begin with, this driver is extremely crudely implemented. The short version of some of the issues surrounding this is: past tech bloggers have discovered after doing a deep dive that the IOCTLs (input/output controls) of this driver can call for a SMI (system mode interrupt), and what’s worse, they can make these calls through user space. While I have not confirmed what from this current update would have caused this to crash games and the like, this is definitely why this driver always comes up in Anti-Cheat software discussions for games and instability discussions in other software, and I have a solid hypothesis that whatever the exact reason, Windows’ security and vulnerability tightening has absolutely amplified this problem. I plan to do a deeper dive of my own into this current update’s changelog, and I will report my own findings here once I do. If you’re curious about more details, I highly suggest reading StarkeBlog’s incredibly thorough examination of this driver on their own post here.
Now that I’ve gone over some of the what and potentially why, here’s the important “how” – how to address the issue, both proactively, or if you’ve already installed the new update.
Detecting and stopping the driver
Thankfully detecting the driver if it was OEM-installed or properly registered to the OS is extremely easy – it’s as simple as going to your System32 folder in your File Explorer and searching for the physical file there. Most Windows system folders will be located in C:/Windows/System32 – simply go there and scroll down to see if you see the file. If you do, DO NOT just start trying to delete things! There is a simple but particular process to handle this, and I will cover it in steps.
The first thing to mention is: while you likely do not use this driver for anything serious, there is always a chance when you mess with drivers that you will cause system or hardware instability. While this is a very reversible fix, do keep in mind that this may occur, and since I can’t look at everyone’s particular setup, know and understand these risks before continuing to troubleshoot this!
NOTE: Before making system-level changes, ALWAYS back up your important data and create a System Restore point! This is not a highly destructive change but it is better to be safe than sorry!!
1. The easier and more secure method – Microsoft Sysinternals:
* Download and run the “Autoruns” Microsoft Sysinternals tool. Be sure to run it as an administrator. NOTE: This is a Microsoft program and should only be downloaded from this link or a trusted repo. NEVER EVER download paid driver software from a company that you do not trust – there’s no good reason, and many of these are scams!
* Once this tool is open, go to the “Driver” tab, find “inpoutx64” in the driver list and uncheck it.
* Restart your computer. When your computer reboots, verify all your hardware works as expected, and test the problem to see if crashes have stopped. You can reopen this tool at any time to be sure that the driver is disabled.
2. The manual method – Command Prompt:
* Search for your Windows Terminal in your Start Menu, right click it, and run it as administrator. Make sure you are in Command Prompt mode.
* Type the following commands:
sc stop inpoutx64
sc delete inpoutx64
* Those commands will stop and delete the driver in your driver store. DO NOT delete the physical file in System32 yet.
* Restart your computer. When your computer reboots, verify all your hardware works as expected, and test the problem to see if crashes have stopped.
* If after a few days this seems to have fixed your problem without issues, you can run your PC in Safe Mode and delete the driver manually, but honestly there should be no need for this and I don’t recommend it – if you want that peace of mind, use the above method instead.
3. The manual method – PowerShell:
(This step is coming soon!)
From then on, whether you have the update or you don’t, you should be all set. If you don’t have the update, it should as of now be safe to proceed with installing it and you should not see those reported instability issues. And there you have it!
I plan on updating this soon as well as adding a little mini-opinion piece to it, but for now at least you have the info to make the decision on how you want to tackle this issue. Please also note that this only affects that one instability issue with gaming – this will not fix any other bugs in that update, such as Windows Hello PIN issues and the like, though those do seem to be pretty rare at the moment.
Photo credit: Daniel Eliashevskyi, Unsplash
(All photo use not made by me was checked to be genAI contribution-free to the best of my ability.)
