CVE-2023-45283

The filepath package does not recognize paths with a ??\ prefix as
special. On Windows, a path beginning with ??\ is a Root Local Device path
equivalent to a path beginning with \?. Paths with a ??\ prefix may be
used to access arbitrary locations on the system. For example, the path
??\c:\x is equivalent to the more common path c:\x. Before fix, Clean
could convert a rooted path such as \a..??\b into the root local device
path ??\b. Clean will now convert this to .??\b. Similarly, Join(, ??,
b) could convert a seemingly innocent sequence of path elements into the
root local device path ??\b. Join will now convert this to .??\b. In
addition, with fix, IsAbs now correctly reports paths beginning with ??
as absolute, and VolumeName correctly reports the ??\ prefix as a volume
name. UPDATE: Go 1.20.11 and Go 1.21.4 inadvertently changed the definition
of the volume name in Windows paths starting with ?, resulting in
filepath.Clean(?\c:) returning ?\c: rather than ?\c:\ (among other
effects). The previous behavior has been restored.

Notes