The Internet Systems Consortium released a security advisory on Monday about a possible denial of service attack against BIND named DNS servers (which constitute the majority of name servers on the internet).  The advisory states that the primary threat is against recursive name servers (the ones clients workstations/laptops/mobile devices point to to translate DNS names into IP addresses), though authoritative primary and secondary name servers could also be at risk if configured with experimental record types.  While they were not aware, at the time, of any active exploitation of the vulnerability, the details had been discussed in public mailing lists.  The vulnerability involves improper handling of certain requests with zero-length RDATA fields.  From the description, it doesn't appear that the crafting of a packet that would trigger the vulnerability would be too difficult.  The result would be either crashing the named daemon or disclosure of some unrelated contents of memory.  Updates should be applied, especially to your recursive name servers, as soon as practical.

References:

http://www.isc.org/software/bind/advisories/cve-2012-1667

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-1667

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Jim Clausing, GIAC GSE #26
jclausing --at-- isc [dot] sans (dot) edu