Bugtraq mailing list archives
Re: Permitting recursion can allow spammers to steal name server resources
From: Mark Johnston <mjohnston () skyweb ca>
Date: Wed, 10 Sep 2003 13:21:54 -0500
Chris Brenton <cbrenton () chrisbrenton org> wrote:
Changing Bind so that it will not act recursively for all hosts on the Internet is a relatively simple process. Edit the /etc/named.conf file to add in the "allow-recursion" parameter similar to the following: options { directory "/var/named"; allow-recursion {localnets; }; }; All other subnets however will be blocked from doing recursive queries. Users on the Internet will only be permitted to look up information you are authoritative for (like your Web server's IP address, your MX record, etc.).
That's not entirely true. BIND (9, at least) is still vulnerable to cache poisoning by local users, after which it will serve up the cached answers to anyone that can query (not just recursion-authorized clients.) Try looking up a domain you aren't authoritative for from a recursion-authorized client, then from an unauthorized one. You'll get the cached answer with the unauthorized client. Of course, given an ISP or corporation, it's trivial to make one of their users look up your hostname. The rationale, as I understand it, is that returning a cached answer doesn't require recursion, so allow-recursion doesn't apply. The proper way to avoid this problem is to configure BIND to deny all queries except ones you specifically want to answer: options { allow-query { localnets; }; allow-recursion { localnets; }; }; zone "example.com" { # An authoritative zone allow-query { any; }; # other example.com statements }; Mark
Current thread:
- Permitting recursion can allow spammers to steal name server resources Chris Brenton (Sep 10)
- Re: Permitting recursion can allow spammers to steal name server resources Mark Johnston (Sep 10)
- Re: Permitting recursion can allow spammers to steal name server resources Greg A. Woods (Sep 10)
- Re: Permitting recursion can allow spammers to steal name server resources Dan Harkless (Sep 10)
- Re: Permitting recursion can allow spammers to steal name server resources Mike Hoskins (Sep 10)
- Re: Permitting recursion can allow spammers to steal name server resources Devin Nate (Sep 15)