Date: Fri, 9 Feb 2001 13:36:15 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: Borja Marcos <borjamar@sarenet.es> Cc: freebsd-security@FreeBSD.ORG Subject: Re: nfsd support for tcp_wrapper -> General RPC solution Message-ID: <20010209133615.P26076@fw.wintelcom.net> In-Reply-To: <3A83C933.8F89DC69@sarenet.es>; from borjamar@sarenet.es on Fri, Feb 09, 2001 at 11:40:51AM %2B0100 References: <Pine.BSF.4.33.0102091125000.59792-100000@deneb.dbai.tuwien.ac.at> <3A83C933.8F89DC69@sarenet.es>
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* Borja Marcos <borjamar@sarenet.es> [010209 02:41] wrote: > Gerald Pfeifer wrote: > > > > On Tue, 30 Jan 2001, Alfred Perlstein wrote: > > >> Or are we just missing something? > > > Missing the fact that nfsd is an in-kernel process and therefore > > > pretty hard to link against libwrap. > > > > Hard, or impossible? ;-) > > Well, nfsd must serve requests at high speed. Having it > call TCP Wrapper can be a big overhead, depending on how you have > configured /etc/hosts.allow and /etc/hosts.deny > > I was thinking about a different (and general) solution, but I > have had no time to implement it. Perhaps I will try to find some time. > > The trick is to use the portmapper with TCP Wrapper with a slight > twist. You keep a set of firewall (ipfw or ipfilter) rules in a file, > and whenever portmap receives the RPC service registration from the > daemon, it "runs" the ipfw or ipfilter configuration > script passing it the port number where the service has registered. > > This provides good protection for *any* RPC service, > you don't need to tinker with RPC daemons -only the portmapper- > and the overhead is minimal: only a call to the TCP Wrapper library > whenever a service registers itself to the portmapper. This is a really flawed idea. All portmap does is provide a name/version/protocol mapping of a service to a tcp/udp port. One can trivially do a portscan of a box running RPC services and figure out which are open. You don't need portmap to brute force finding out where a remote vulnerable service is located. In fact because afaik NFS always uses a well known port, you really don't need portmap to map it, you just need to use the port, portmapper for NFS is just a formality. Ok, with that out of the window, we _could_ consider mucking userland mountd to use tcpwrappers to graft an ACL to what's in /etc/exports. This is also a bad idea, one can just brute force the NFS cookie/filehandle required to gain access, then contact the NFS port. The solution is to use a firewall. -- -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org] "I have the heart of a child; I keep it in a jar on my desk." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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