Project Zero: Who Contains the Containers?
This is a short blog post about a research project I conducted on Windows Server Containers that resulted in four privilege escalations which Microsoft fixed in March 2021. In the post, I describe what led to this research, my research process, and insights into what to look for if you’re researching this area.
Windows 10 and its server counterparts added support for application containerization. The implementation in Windows is similar in concept to Linux containers, but of course wildly different. The well-known Docker platform supports Windows containers which leads to the availability of related projects such as Kubernetes running on Windows. You can read a bit of background on Windows containers on MSDN . I’m not going to go in any depth on how containers work in Linux as very little is applicable to Windows.
The primary goal of a container is to hide the real OS from an application. For example, in Docker you can download a standard container image which contains a completely separate copy of Windows. The image is used to build the container which uses a feature of the Windows kernel called a Server Silo allowing for redirection of resources such as the object manager, registry and networking. The server silo is a special type of Job object , which can be assigned to a process.
