Re: FreeBSD listen()

[poptix () POPTIX NET (Matthew S. Hallacy)]

On Thu, 28 Oct 1999, CyberPsychotic wrote:

> ~ :This fact causes problems. Some application (for example ftp server in
> ~ :passive mode or ftp client in active mode) use
> ~ :listen(data, 1);
> ~ :accept(data,...);
> ~ :close(data);
> ~ :to  limit  the  number of incoming data connections to exactly one. If
> ~ :second  connection  is not rejected it makes possible attack to inject
> ~ :or  intercept  data  between  server  and  client  as described in NAI
> ~ :bulletin
>
> That is a ftp daemon/client(depending whether it's an active or passive
> mode), which should take care of accepting only single connection and only
> from proper source (which is surprisely being ignored by some daemons,
> such as ncftpd f.e.).
Some programs, such as fxp rely on this kind of behaviour, while i agree
that there should be checking, we dont want to break good programs ...

>               However even ncftpd closes all the incoming
> connections to the port once the first one has been accepted. Same goes
> with my ftp client. (shipped r.h. 6.0). So I don't think there're any
> security issues except syn-flooding, are involved here.