[Freeswitch-users] Thoughts on security/code injection/etc. in FS when allowing user supplied data

[Daniel Ivanov]

I am glad to see someone is concerned about input validation when it comes
to voip. It is much neglected when we're constructing our services, partly
due to the fact that it's still considered black magic. I believe that
system and bgsystem should be strictly regulated and  ani and sip vars
should be safe-parsed before feeding to a turing machine. Security through
obscurity has never worked and i beth my both legs we all have a few
vulnerable applications behind our backs. Let's unite to make FS the most
stable and secure softswitch out there.
On May 19, 2013 5:21 PM, "Nathan Neulinger" <nneul at mst.edu> wrote:

> I've noticed several places in FS code and examples where it isn't safe at
> all to take user supplied data.
>
> An easy example is the use of mailer_app:
>
>
> #ifdef WIN32
>      switch_snprintf(buf, B64BUFFLEN, "\"\"%s\" -f %s %s %s < \"%s\"\"",
> runtime.mailer_app, from,
> runtime.mailer_app_args, to, filename);
> #else
>      switch_snprintf(buf, B64BUFFLEN, "/bin/cat %s | %s -f %s %s %s",
> filename, runtime.mailer_app, from,
> runtime.mailer_app_args, to);
> #endif
>
> another is ANY use of passing channel vars or data to a system or bgsystem
> command.
>
>
> This isn't an issue normally, but if you want to give limited ability for
> users to control their own dial rules, then
> you wind up having to be very careful with processing the data to make
> sure it's safe. That's always a good idea, but it
> still seems like a bad idea to take that data and then directly use it in
> a completely unsafe context like a parsed
> command line.
>
> For the voicemail notify case, seems like an easy answer would be
> something like a "vm-notify-hook", which at that
> point, could call out to lua or perl to do the actual sending in a safe
> manner, passing the recipient/sender/etc. as
> data instead of on cmd line.
>
> For the 'passing channel vars...' case, I think it would be good to have a
> 'system_json' and 'bgsystem_json' set of
> routines that would pass channel data to the script on stdin in json
> format.
>
> Regardless of implementation of either of those, I think it would be
> worthwhile to have a shell_escape() routine in the
> core utilities to allow the current syntax to be used more safely.
>
> -- Nathan
>
> ------------------------------------------------------------
> Nathan Neulinger                       nneul at mst.edu
> Missouri S&T Information Technology    (573) 612-1412
> System Administrator - Architect
>
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