Use-After-Free in win_close()

Date: 16.11.2023
Severity: Low

When closing a window, vim may try to access already freed window
structure. So before trying to access any window related variable
verify that the window to be closed is still valid and if not, return.

Impact is low, since it is not very easy to make use of this
and execute some payload (in particular not, without the
user noticing).

The Vim project would like to thank Fabian Toepfer for reporting this issue
which is now fixed in Vim patch 9.0.2106.

URL: 25aabc2