‘RedSun’ flaw in Microsoft’s security software lets hackers take over your PC. Here’s how to protect it.

Microsoft Windows is one of the most popular operating systems on the planet, second only to Android. With 1 billion users spread out across interests and industries, robust security software is critical to keeping personal files and private information safe. Unfortunately, a newly discovered flaw in Windows’ built-in Microsoft Defender could give hackers full access to a PC without the user’s knowledge.

What is Microsoft Defender?

Windows PCs didn’t always have antivirus protection built in. In fact, Microsoft’s first-party solution didn’t come along until 2006, 21 years after Windows debuted. Today, the aptly named Microsoft Defender ships on every PC from Windows Vista all the way to Windows 11.

The purpose of Microsoft Defender is simple: It is designed to protect your PC from the usual online threats that pervade the internet. This includes viruses, malware, ransomware, and phishing attacks. Microsoft even boasts that Defender “can block almost all malware at first sight, in milliseconds.”

That sounds promising.

In short, it provides a necessary layer of protection in a world of increasingly dangerous cyberattacks driven by AI. Unfortunately, while Microsoft Defender is meant to minimize hacking threats, it can now be used to infiltrate a PC wholesale.

Microsoft Defender’s fatal flaw

An anonymous researcher who goes by “Chaotic Eclipse” discovered a major flaw in Microsoft Defender. Dubbed “RedSun,” the threat can lead to hackers gaining administrative privileges to a target PC without the user’s knowledge or permission.

RedSun affects a wide range of PCs running Windows 10 and Windows 11.

With administrative privileges, a hacker can essentially control every aspect of the user’s PC. This includes installing or uninstalling software, running programs, changing user settings, modifying user accounts, resetting system passwords, disabling security software and firewalls (including Defender itself), and accessing user files.

RedSun, at its core, is a form of malware — the same kind that Microsoft claims to block in the blink of an eye. Then again, the company did say that Defender stops “almost all malware,” so there’s some wiggle room. It just so happens that this particular bug that the system missed comes with potentially devastating consequences.

Staying true to the name, Chaotic Eclipse left detailed instructions on a GitHub page, explaining how hackers can use the exploit to raise awareness of the issue. The move is a double-edged sword for users and Microsoft alike. On one hand, Chaotic Eclipse hopes that with this information divulged, Microsoft will patch Defender promptly to keep all 1 billion users safe around the world. On the other hand, these instructions tell hackers exactly how to infiltrate PCs using the Microsoft Defender exploit, potentially leading to mass cyberattacks of critical systems — from personal computers to businesses and even government agencies — that run on Windows.

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RedSun affects a wide range of PCs running Windows 10 and Windows 11, as well as Windows Server for enterprise applications.

How to protect your PC from RedSun

At the time this article was published, there is currently no fix available for RedSun, and it could take weeks or even months for Microsoft to issue an update. Since the exploit is now openly available and receiving attention from the media, we hope this spurs Microsoft to act fast, but considering all the bugs that have plagued Windows 11 lately — including this BitLocker hole we covered earlier this year — the company already has its hands full.

While you may not be able to stop a hacker from breaching your PC through Microsoft Defender, you can add an extra layer of protection by temporarily installing a trusted third-party antivirus solution. Some options include McAfee, Bitdefender, and Norton.

In the meantime, keep an eye on the Windows Update page in the Settings app on your PC for the latest bug fixes that will finally put RedSun to rest. Of course, if all else fails, there’s always Mac!