TCP/BGP vulnerability - easier than you think

Wed Apr 21 13:21:13 UTC 2004

On Wed, Apr 21, 2004 at 03:09:15PM +0200, Iljitsch van Beijnum wrote:
> >> The good part here is that filtering RSTs should still work.
> 
> > It doesn't. The RST are then being sent by the authorized sender and
> > your edge anti-spoof filtering for RST doesn't help a single 
> > millimeter.
> 
> Now it's your time to overlook something: the filters I listed in my 
> earlier message simply filter RSTs to/from the BGP port without looking 
> at the address fields. Filtering ALL RSTs is probably a bad idea as 
> broken sessions will then have to time out, possibly inconveniencing 
> users (and thereby generating support calls).

As you didn't specify where to apply these filters, I guessed on the
edges. I would have never thought that someone would really suggest
to deliberately break RST for valid BGP sessions.

> So I believe filtering out all BGP RSTs on all edges is 
> probably a good idea.

RST and SYN. But that's still patchwork. Do anti-spoofing filtering
in general, not only mitigating _this_ thread. Don't allow packets
from source IPs of your originated IP spaces enter your network,
ADDITIONALLY to securing the transport via TCP MD5 authentication or
even better with IPSEC. Having always two lines of defense is good
security practise, especially if the doors to properly close are
many (edge interfaces).