Re: unused bit attack alert

[antirez () LINUXCARE COM (antirez)]

On Mon, Feb 21, 2000 at 02:36:17PM -0800, Vern Paxson wrote:
> > LigerTeam, strongly propose inserting of
> > solution code before the computing of flag
> > variable.
> >
> >   flag = flags & 0x3f;
>
> Otherwise you are still vulnerable to attackers setting legitimate flags
> in bogus combinations, such as adding URG to a SYN.

Also since the valid TCP flags combinations are fixed
and just ~ 13 at cost of some overhead you can simply
allows only this. An example is the ipt_unclean netfilter
module.
For LigerTeam: this is a known problem, please don't claim
you have discovered it (see BUGTRAQ archive).

antirez

--
Salvatore Sanfilippo, Open Source Developer, Linuxcare Italia spa
+39.049.8024648 tel, +39.049.8036484 fax
antirez () linuxcare com, http://www.linuxcare.com/
Linuxcare. Support for the revolution.