oss-security - Re: DNS vulnerability: other relevant software

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Date: Wed, 09 Jul 2008 20:13:02 +0200
From: Florian Weimer <fw@...eb.enyo.de>
To: oss-security@...ts.openwall.com
Subject: Re: DNS vulnerability: other relevant software

* Mark J. Cox:

>> Additionally, Debian has noted (DSA 1605-1) that the GNU libc stub
>> resolver could benefit from random query source ports as well, but
>> no patches are currently available to implement this:
>
> Note that GNU libc stub resolver when used with a recent kernel
> (2.6.24+) will give you random UDP source ports on each request
> because of this Linux commit:
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=32c1da70810017a98aa6c431a5494a302b6b9a30

Is net_random() cryptographically secure?  The paper referenced in the
source doesn't talk about this.

> Vendors may with to consider backporting that kernel patch as an
> effective mitigation without requiring glibc changes (and with the
> advantage of being able to be have a customized range using
> ip_local_port_range etc)

This still leaves the transaction ID generation to deal with.  It's
rdtsc on amd64 (don't know if this is good enough), but
gettimeofday-based on some other architectures.

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