Steps have finally been taken by Microsoft to protect millions of exposed networks vulnerable to a .Net exploit that was first discovered nine months ago.During that time many customers were not only left in the dark, but left dangerously exposed by the vulnerability which was a null byte exploit.
The company has tried to patch the exploit since its discovery by analyst group Security-Assessment.com last October, and has kept mum on the flaw which was uncovered in the US this week as a result of Patch Tuesday.
Security consultant and researcher at Security-Assessment.com Matthew Strahan said a filename which contains a null byte in the .Net environment can launch a Null byte injection attack which allows servers to be fully compromised.
He said a flaw exists in an upload file code when the .Net Common Language Runtime (CLR) considers Null bytes as data to directly call a native C function call.
"The flaw could be very dangerous when affected servers are trying to receive uploaded files; a null byte will terminate strings in lower level layers but won't for strings in higher level layers," Strahan said.
"The attack means you can upload any code you want to take over the entire server.
"If you upload a .aspx file, followed by a Null byte and an extension such as .txt, it will be saved as a txt file. [Native function] calls at the injected Null byte allows a remote user to terminate a sting parameter which can lead to a compromise."
