After several public discussions and the swift patching of Apple iTunes, Microsoft has issued the security advisory KB2269637 to address DLL Hijacking or Preloading vulnerabilities within all versions of Microsoft Windows. This advisory covers a 10 year old flaw within the Windows operating system and how it handles the loading of Dynamic Link Libraries (.DLL or .SYS) files using LoadLibrary and SearchPath API calls. When an application attempts to load a library without specifying the full path, Microsoft Windows will perform a DLL search in order to load the file. Based off the current Microsoft DLL ‘Safe’ Search Order specifications, the order is as follows:
- The directory from which the application loaded
- The system directory
- The 16-bit system directory
- The Windows directory
- The current working directory
- The directories that are listed in the PATH environment variable
- Upon opening a file, the vulnerable application changes the current working directory to the destination directory of the last opened file.
- An application attempts loads a DLL without specifying a full path of the target DLL.
- Windows searches through the directories in the DLL Search Order and discovers the DLL in the current working directory where the opened file resides.

Scott Lang, Sr. Director, Product Marketing at BeyondTrust
Scott Lang has nearly 20 years of experience in technology product marketing, currently guiding the product marketing strategy for BeyondTrust’s privileged account management solutions and vulnerability management solutions. Prior to joining BeyondTrust, Scott was director of security solution marketing at Dell, formerly Quest Software, where he was responsible for global security campaigns, product marketing for identity and access management and Windows server management.