Re: DNS ACL ?

[Chris Brenton <cbrenton () chrisbrenton org>]

On Fri, 2005-11-11 at 08:35 -0500, John Hally wrote:
> I need a sanity check regarding DNS ACLs.  For external facing DNS servers
> you need to allow only udp/53 inbound, correct?  I know tcp/53 is used for
> zone transfers and requests/replies greater than a certain size, but they
> shouldn't typically happen for general dns queries correct?  

Correct. Typically what gets people into trouble is when they create a
PTR record that associate a dozen+ host names with a specific IP
address. If you are not doing this, you are probably fine.

Quick test would be to use dig to run through all the queries you want
resolvable from the Internet. If you never get an answer with the
truncation bit set in the DNS header, you are in good shape.

As a side note, make sure all Internet exposed name servers are
_non-recursive_. Cache poisoning, domain parking and a host of other
nasty things can happen otherwise.

HTH,
Chris



------------------------------------------------------------------------------
Audit your website security with Acunetix Web Vulnerability Scanner: 

Hackers are concentrating their efforts on attacking applications on your 
website. Up to 75% of cyber attacks are launched on shopping carts, forms, 
login pages, dynamic content etc. Firewalls, SSL and locked-down servers are 
futile against web application hacking. Check your website for vulnerabilities 
to SQL injection, Cross site scripting and other web attacks before hackers do! 
Download Trial at:

http://www.securityfocus.com/sponsor/pen-test_050831
-------------------------------------------------------------------------------