Actually, from the looks of the tweet linked above, it seems to allow a user to chown an arbitrary system file so that it is owned by him, in that case the shad

Actually, from the looks of the tweet linked above, it seems to allow a user to chown an arbitrary system file so that it is owned by him, in that case the shadow file. Having access to the shadow file would allow the user to trivially reset the password for every account on the machine, including root. With that access, a user could then do just about anything to the box, and then reset the password/shadow file back to its old value/permissions so that sysadmins would be none the wiser.