MS virtualisation bug dodges defences

A newly discovered flaw in Microsoft's virtualisation technologies creates a potential mechanism for hackers to sidestep security defences.

The unpatched vulnerability creates a possible route around security threat mitigation technologies such as Data Execution Prevention (DEP), Safe Exception Handlers (SafeSEH) and Address Space Layout Randomization (ASLR). The security bypass bug affects Virtual PC but not Microsoft virtualisation products based on Redmond's Hyper-V enterprise-class server technology.

The shortcoming, discovered by Core Security, creates a way for hackers to attack applications provided they are running on a virtual PC. The same applications could not be hit in the same way if they were running on a standard PC or server.

Core went public with the publication of an advisory and proof-of-concept code on Tuesday after back-and-forth discussions with Microsoft over seven months reached an impasse. The security firm reckons the unpatched bug, which involves memory management of Microsoft's Virtual Machine Monitor, opening the way to all sorts of potential problems for systems running Windows Virtual PC, Microsoft Virtual PC 2007 and Virtual Server 2005.

Redmond, by contrast, argues the alleged bug discovered by Core only offers a mechanism to "exploit security vulnerabilities already present on the system, rather than an actual vulnerability", security blogger Ryan Nardine reports.

Windows 7 uses Virtual PC technology to provide backward compatibility with older apps via XP Mode. Microsoft continues to say the use of this technology is safe, as explained in much more depth in a post on Redmond's security response blog here. ®