Cisco Security Advisory – Multiple Cisco products are vulnerable to DNS cache poisoning attacks due to their use of insufficiently randomized DNS transaction IDs and UDP source ports in the DNS queries that they produce, which may allow an attacker to more easily forge DNS answers that can poison DNS caches. To exploit this vulnerability an attacker must be able to cause a vulnerable DNS server to perform recursive DNS queries. Therefore, DNS servers that are only authoritative, or servers where recursion is not allowed, are not affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/68039/cisco-sa-20080708-dns.txt
Source: https://packetstormsecurity.com/files/68039/Cisco-Security-Advisory-20080708-dns.html