Microsoft is warning users of older versions of Windows to urgently apply a Windows Update today to protect against a potential widespread attack. The software giant has patched a critical remote code execution vulnerability in Remote Desktop Services that exists in Windows XP, Windows 7, and server versions like Windows Server 2003, Windows Server 2008 R2, and Windows Server 2008. Microsoft is taking the highly unusual approach of releasing patches for Windows XP and Windows Server 2003 even though both operating systems are out of support. Windows XP users will have to manually download the update from Microsoft’s update catalog.

“This vulnerability is pre-authentication and requires no user interaction,” explains Simon Pope, director of incident response at Microsoft’s Security Response Center. “In other words, the vulnerability is ‘wormable’, meaning that any future malware that exploits this vulnerability could propagate from vulnerable computer to vulnerable computer in a similar way as the WannaCry malware spread across the globe in 2017.”

Attackers will likely start making malware now that patches are out

Microsoft says it hasn’t observed exploits of this vulnerability, but now that the patches are being released it’s only a matter of time before attackers reverse engineer Microsoft’s patches and create malware. Thankfully, Windows 8 and Windows 10 machines aren’t affected by this vulnerability. While Windows 10 is now more popular than Windows 7, there are still millions of machines running Windows 7, so a potential attack could be very troublesome.

Microsoft broke from its tradition of not supplying patches for Windows operating systems that are out of support back when thousands of computers in more than 100 countries were affected by malware known as WannaCry. The malware used flaws in old versions of Windows to encrypt computers and demand a $300 ransom before unlocking it. Microsoft is clearly keen to avoid another WannaCry, even though it says “the best way to address this vulnerability is to upgrade to the latest version of Windows.”