Re: requiring reserved NFS client ports by default

In message <8666AC5F-F797-489F-944D-CD7B4D373766@karels.net>, Mike Karels 
write
s:
> On 16 Apr 2024, at 18:05, Mark Johnston wrote:
>
> > It's common practice for NFS clients to bind to reserved ports (i.e., <=
> > 1023) since some NFS servers require this as a weak security measure
> > against attackers with network access to a server but without local
> > privileges.  FreeBSD's NFS server does not require clients to use
> > privileged ports by default, but this can be changed by setting
> > nfs_reserved_port_only=YES in rc.conf.
> >
> > I would like to propose flipping the default for nfs_reserved_port_only.
> > This raises the bar a bit for a malicious agent able to execute
> > unprivileged code on a machine with network access to an unauthenticated
> > NFS server running FreeBSD.  This behaviour would match the defaults on
> > Linux (the per-export "secure" attribute) and OpenBSD.
> >
> > The downside is increased pressure on the limited range of reserved port
> > numbers.  However, the server will complain on the console if a request
> > arrives on an unreserved port, so diagnosis should be easy, and most
> > clients sport an option to not use a reserved port number (noresvport on
> > FreeBSD), so one can configure client mounts to use them only where
> > needed.  And, the option is easy to disable on the server should that be
> > necessary.  My aim here is to provide a safer out-of-the-box behaviour.
> >
> > Any comments, objections, feedback?
>
> I think this is a good idea.  It should block one class of surreptitious
> access by unprivileged users on a machine in the export list, and there
> doesn't seem to be much downside.
>
> 		Mike

Agreed.


-- 
Cheers,
Cy Schubert <Cy.Schubert@cschubert.com>
FreeBSD UNIX:  <cy@FreeBSD.org>   Web:  https://FreeBSD.org
NTP:           <cy@nwtime.org>    Web:  https://nwtime.org

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