Microsoft rushes to patch critical flaw affecting every Windows PC

Microsoft has been forced to issue a critical patch for a vulnerability that affects every current version of its Windows operating system.

The bug affects code in the Microsoft secure channel (schannel) security component. This component implements the secure sockets layer and transport layer security (TLS) protocols.

A flaw in the code means it fails to properly filter specially formed packets allowing hackers to execute code remotely on an affected Windows machine.

According to the advisory, the flaw affects Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7, Windows 8/8.1, Windows Server 2012/2012 R2, and Windows RT/RT 8.1 machines. The flaw is rated critical for all affected operating systems.

Microsoft said that it "had not received any information to indicate that this vulnerability had been publicly used to attack customers".

Security researchers said exploitation of the SChannel bug has the potential to be worse than Heartbleed and Shellshock combined due to the large numbers of affected systems.

"Heartbleed was less powerful because it was just' an information disclosure bug and Shellshock was remotely exploitable only in a subset of affected systems," said Craig Young, security researcher at Tripwire.

"Some administrators may want to prioritise this over the Internet Explorer patch even though we've seen attacks we've seen in the wild against the browser. This is because MS14-066 has the potential to be exploited without user-interaction," he said.

Young added that exploitation of the bug would be "tricky". "Hopefully, this will give admins enough time to patch their systems before we see exploits."

Just last week, Microsoft was preparing a slew of updates to its products with 16 patches to fix critical flaws in Windows and Internet Explorer.