Since a low privileged user has full control over the QueuedPresentations and InvalidPresentations folders, it is possible to create an invalid presentation in the QueuedPresentations folder and then place a symbolic link for that file name in the InvalidPresentations folder that points to a privileged location. When the service checks for presentations, it will move the file out of the QueuedPresentations folder and into the InvalidPresentations folder. When it does so, the service will hit the symbolic link and write the new file into a protected location with permissions that allow the low privileged user full control over the contents, resulting in Elevation of Privilege to NT AUTHORITY\SYSTEM.
When assessing software for privilege escalation vulnerabilities, finding a starting point can often be overwhelming as there are many different primitives and vulnerability classes that exist. My approach often includes starting with the basics and working my way up in complexity. This process typically involves running a tool such as PowerUp, which will identify various trivial (yet common) misconfigurations. If nothing interesting is returned, the next step is often looking for logical vulnerabilities specifically abusing symlink/mountpoint/hardlink primitives. In order to quickly identify potential vulnerabilities that could be exploited with the linking primitives, we need to identify locations on the OS where a privileged process (often SYSTEM) is interacting with a folder or file that a low privileged user has control over.
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