A toolkit designed to exploit a recently-disclosed Microsoft JPEG vulnerability has been released onto the net. The toolkit (screen shot from AV firm F-Secure here) makes it trivially easy for maliciously-minded attackers, however unskilled they might be, to exploit unpatched Windows systems and run malicious code.
The attack mechanism used here takes advantage of a recently discovered flaw in the way Microsoft applications process JPEG image files. Malformed JPEG files are capable of triggering a buffer overflow in a common Windows component (the GDI+ image viewing library), it was revealed last week. This behaviour creates a ready mechanism to inject exploit code into vulnerable systems. Windows XP and Windows Server 2003 make use of vulnerable library by default. Other Windows OSes might be vulnerable, depending on what applications users have installed.
Microsoft, which unsurprisingly rates the vulnerability as critical, released a patch to defend against the flaw on 14 September. To be at risk, users have to open a JPEG file modified to trigger the flaw using either IE or Outlook. They also need to be unpatched. Unfortunately there's plenty of scope for both conditions to be met and the gene pool of potential victims is huge.
The problem is exacerbated by the fact JPEG files are typically viewed "as a benign and trusted file format... as such it is possible to cause image files to be viewed with minimal user-interaction through several applications including many email clients such as Outlook and Outlook Express," Security tools vendor ISS notes. "There is also potential for automatic exploitation in the form of a network-propagating worm."
Since the Microsoft's update security firm ScanSafe, which looks for malware in web traffic, has stopped numerous JPEG files identified as containing the exploit.
Users are strongly advised to download and install the latest software patches from Microsoft and to update their anti-virus definitions as soon as possible. If you haven't done it already now would be a very good time. Sysadmins need to include the contents of JPEG files among the types of traffic scanned by network security tools. Several gateway AV scanners, for example, do not inspect image files by default. ®