This fixes a bug that allows others to write to remote users pseudo terminals. Looking at the revision 1.29 commit message and thread[2] that led to this bug I'm pretty sure that it wasn't intended to be this way.
[1] https://marc.info/?t=140913893700009&r=1&w=2 Index: sshpty.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/sshpty.c,v retrieving revision 1.29 diff -u -p -r1.29 sshpty.c --- sshpty.c 3 Sep 2014 18:55:07 -0000 1.29 +++ sshpty.c 30 Jul 2015 10:31:30 -0000 @@ -142,7 +142,7 @@ pty_setowner(struct passwd *pw, const ch /* Determine the group to make the owner of the tty. */ grp = getgrnam("tty"); gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid; - mode = (grp != NULL) ? 0622 : 0600; + mode = (grp != NULL) ? 0620 : 0600; /* * Change owner and mode of the tty as required.
