sudo -- Privilege escalation with sudoedit

Todd Miller reports:

When sudo performs its command matching, there is a special case
for pseudo-commands in the sudoers file (currently, the only
pseudo-command is sudoedit). Unlike a regular command,
pseudo-commands do not begin with a slash (‘/’). The flaw is that
sudo’s the matching code would only check against the list of
pseudo-commands if the user-specified command also contained no
slashes. As a result, if the user ran “sudo ./sudoedit” the normal
matching code path was followed, which uses stat(2) to verify that
the user-specified command matches the one in sudoers. In this
case, it would compare the “./sudoedit” specified by the user with
“sudoedit” from the sudoers file, resulting in a positive
match.