[CentOS] Re: Securing serial ports - fax modems

Scott Silva ssilva at sgvwater.com
Fri Jul 25 21:25:39 UTC 2008

on 7-25-2008 1:27 PM James B. Byrne spake the following:
> I have already deployed a fax server and am about to deploy a backup
> system for this host at our off-site facility.  It struck me that I have
> given no thought to securing the serial port to unauthorized access.  The
> modem is a Multi-Tech MT5634ZBA which supports data as well as fax.  So
> this poses the same type of risk, if not to the same degree, as an ssh or
> telnet port but without the availability of a firewall to throttle
> repeated unsuccessful connection attempts.
> Are there any recommendations on what should be done in this circumstance
> or am I fretting unduly?
> Regards,
If the system doesn't answer the data attempts, you should only have to worry 
if someone can send a crafted bit of data that will trigger a buffer overflow 
when the "fax image" is processed. I haven't heard of one, though.

You might be able to turn off the modems ability to answer any capabilities 
but fax, and Class 1 fax AFAIR doesn't support a data channel. Only Class 2.0.

MailScanner is like deodorant...
You hope everybody uses it, and
you notice quickly if they don't!!!!

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