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Date:      Mon, 08 Apr 2002 18:14:19 GMT
From:      "Peter C. Lai" <sirmoo@cowbert.2y.net>
To:        "Michael Sharp" <ms@probsd.ws>
Cc:        freebsd-security@FreeBSD.ORG
Subject:   Re: Berkley Packet Filter
Message-ID:  <20020408181419.9260.qmail@d188h80.mcb.uconn.edu>
In-Reply-To: <1074.192.168.1.2.1018254621.squirrel@probsd.ws> 
References:  <1074.192.168.1.2.1018254621.squirrel@probsd.ws>

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disabling bpf only prevents someone from running a sniffer on
*your* box should they obtain a shell. I don't see how disabling
it prevents nmap from running syn/fin scans. 

Furthermore, if someone obtains root shell, they could just
load a kernel module to enable bpf-like capabilities. 

In addition, disabling bpf also breaks DHCP (and/or PPP?). If your host gets 
an IP via DHCP (e.g you are running dhclient(1)) you need to enable bpf. 

Michael Sharp writes: 

> It is my understanding that if you comment OUT the bpf line in the kernel
> and re-compile, this disables things like nmap and prevents a sniffer from
> running on the network * easily * correct? 
> 
> The reason I put * easily * in there is because I am aware of other ways to
> bypass bpf, but I believe disabling would defeat 99% of the script kiddies. 
> 
> Michael 
> 
>  
> 
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 -----------
Peter C. Lai
University of Connecticut
Dept. of Residential Life | Programmer
Dept. of Molecular and Cell Biology | Undergraduate Research Assistant
http://cowbert.2y.net/
860.427.4542 (Room)
860.486.1899 (Lab)
203.206.3784 (Cellphone) 


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