IIRC in past there were small part of Windows NT or XP kernel source code leaked. Definitely not the entire OS.
Windows XP and Server 2003 compiled from leaked source code https://www.bleepingcomputer.com/ne...server-2003-compiled-from-leaked-source-code/
Source code for some important files of Windows XP are missing unfortunately. This leak will probably make it easier for projects such as 0patch to investigate some issues.