Since we released Security Advisory 2269637 on August 23, we’ve continued to conduct an investigation not only into our own affected products, but also into how we can best help to protect customers given DLL preloading also affects some third-party applications. We’d like to provide an update on our investigation.
First, I want to be clear that Microsoft plans to address those of our products affected by this issue in the most appropriate way for customers. This will primarily be in the form of security updates or defense-in-depth updates. Also, due to the fact that customers need to click through a series of warnings and dialogs to open a malicious file, we rate most of these vulnerabilities as important.
One of the goals we have at Microsoft is to make it easy for developers to create secure applications on our platform. As we stated in our previous blog post, DLL preloading is a well-known class of vulnerabilities and we have had guidance for developers in place for quite some time. We have recently updated that guidance to provide more clarity.
Even with improved guidance, we recognize that it may take quite a bit of time for all affected applications to be updated and for some, an update may not be possible. With the advisory, we released a tool to help customers protect their systems (see KB 2264107). This tool provides a framework for customers to modify the behavior of the DLL search path algorithm and essentially block unsafe DLL loading. When installed, this tool still needs to be configured in order to block malicious behavior, and customers have asked us for our recommended setting. As a result, our Security Research & Defense team has written a detailed blog post on this topic and has worked with our Microsoft Fix-it team to develop a Fix-it to enable our recommended setting which blocks most network-based attack vectors. (Please note that the tool needs to be installed prior to enabling the Fix-it.)
Many enterprise customers have asked us to make it easier for them to deploy this tool. As a result, we are working with the Windows Update (WU) team to add the tool to the WU catalog. This will make it easier for those running Windows Server Update Services (WSUS) to deploy. We are working to have that solution in place within the next couple of weeks. We are also considering releasing this solution more broadly via WU as a defense-in-depth update for all customers in an “off by default” state. We will share more information through the MSRC blog as our plans are solidified.
Customers should note that the tool is limited to protecting against DLL preloading only and does not protect against .exe files that do not properly load files via a fully qualified path and developers will be required to update those applications accordingly.
Group Manager, Response Communications