On 2024-03-28, Marc SCHAEFER wrote: >> Apparently the root of the security issue is that wall is a setguid program? > > a) wall must be able to write to your tty, which is not possible > if wall is not installed setguid OR if people have sane permissions > on their terminals (e.g. set to mesg n)
Found in /etc/login.defs : # # Terminal permissions # # TTYGROUP Login tty will be assigned this group ownership. # TTYPERM Login tty will be set to this permission. # # If you have a "write" program which is "setgid" to a special group # which owns the terminals, define TTYGROUP to the group number and # TTYPERM to 0620. Otherwise leave TTYGROUP commented out and assign # TTYPERM to either 622 or 600. # # In Debian /usr/bin/bsd-write or similar programs are setgid tty # However, the default and recommended value for TTYPERM is still 0600 # to not allow anyone to write to anyone else console or terminal # Users can still allow other people to write them by issuing # the "mesg y" command. TTYGROUP tty TTYPERM 0600 My tty is set to 0600 and even with "mesg y" only root can send a message with wall. Am I missing something ?