Major Windows 10 security flaw leaves your PC vulnerable – but there’s a quick fix

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It has recently emerged that Windows 10 is suffering from a very serious security flaw that’s preventing the Windows Sandbox and Windows Defender Application Guard (WDAG) from opening – which is leaving some PCs vulnerable to attack.

In case you’ve never heard of them, these two features are important tools that can keep your Windows 10 PC safe, so if they are failing to start, that’s pretty concerning.

Windows Sandbox is a tool that allows you to run applications in an isolated environment away from your system files and settings. If you were to run a malicious app in Windows Sandbox, it would not be able to access your important and private files.

Meanwhile, Windows Defender Application Guard is a tool that is used to protect people using Windows 10’s default web browser, Edge, from online attacks.

According to Microsoft (as reported by TechDows), PCs running Windows 10 Pro and Windows 10 Enterprise, versions 1903, 1909, and 2004 (the three latest updates to Windows 10) are affected.

What happens and how to fix it

A support document from Microsoft states that the two apps will display the following errors when they try – and fail – to start: 

  • E_PATHNOTFOUND (0x80070003)

As you can imagine, having these two important security tools not loading is not good, but the good news is that it can be fixed relatively easily – all you need to do is restart your device and the tools should load normally.

While that is pretty simple, it’s still not ideal, as restarting your PC just to ensure some tools load properly can be disruptive. There’s also the danger that some users will miss the error messages, and continue to use their PCs under the impression that the security tools have loaded correctly.

Microsoft is aware of the issue, however, and is working on a permanent fix for the problem, which will be included in a future Windows 10 update.

Until then, however, you should make sure you keep an eye out for those error messages, and if you rely on those tools, make sure they are running as they are supposed to.

Matt Hanson
Managing Editor, Core Tech

Matt is TechRadar's Managing Editor for Core Tech, looking after computing and mobile technology. Having written for a number of publications such as PC Plus, PC Format, T3 and Linux Format, there's no aspect of technology that Matt isn't passionate about, especially computing and PC gaming. Ever since he got an Amiga A500+ for Christmas in 1991, he's loved using (and playing on) computers, and will talk endlessly about how The Secret of Monkey Island is the best game ever made.