[Dnsmasq-discuss] blocklists, blocking servers, rebind attacks & general aaarrggh
derockwe at akamai.com
Mon Jul 5 11:34:11 UTC 2021
I have a situation for which extending those features would be the exact solution.
On Jul 4, 2021 5:21 PM, Simon Kelley <simon at thekelleys.org.uk> wrote:
On 04/07/2021 21:32, Simon Kelley wrote:
> On 30/06/2021 10:40, Kevin Darbyshire-Bryant wrote:
>> As an ‘experiment’ I tried switching from my own local ‘adblocking’ solution to using an upstream adblocking resolver, eg. cloudflare’s 22.214.171.124 or 126.96.36.199 service.
>> The local adblock solution uses (multiple!) ‘—address/naughtydomain.foo/‘ lines that cause dnsmasq to return ’NXDOMAIN’ - fair enough.
>> Cloudflare (& others I’ve tested) return ‘0.0.0.0’ or ‘::’ instead, not NXDOMAIN. With rebind protection enabled (--stop-dns-rebind), even with --rebind-localhost-ok I get log ’spam’ warning of possible rebind attacks due to the ‘0.0.0.0’ address response.
>> I can turn ‘0.0.0.0’ into NXDOMAIN by using --bogus-nxdomain=0.0.0.0 and that works fine and stops the rebind warnings. However ‘::’ still gets through if an AAAA is specifically requested. There is no equivalent bogus-nxdomain for ipv6.
>> The dnsmasq manpage (under —address) advised "Note that NULL addresses [0.0.0.0 & ::] normally work in the same way as localhost, so beware that clients looking up these names are likely to end up talking to themselves.” Ideally then 0.0.0.0 & :: would both be turned into NXDOMAIN.
>> Should ‘0.0.0.0/32’ be excluded from the rebind checks/accepted by the ‘—rebind-localhost-ok’ option. It’s currently being caught by a ‘0.0.0.0/8’ check.
> I looked at the code that determines private addresses for --bogus-priv
> and rebind: It's a bit unruly for IPv6, so I've rationalised things and
> included :: and 0.0.0.0 in the --rebind-localhost-ok coverage, which at
> least avoids the log spam.
> I wonder if bogus-nxdomain should be extended to IPv6, or we could add
> another option which is the equivalent of
> Or both.
AT the least, bogus-nxdomain should be extended to IPv6, that would
extend --ignore-address too, for free.
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