As warned by Dan Kaminsky, Paul Vixie, and numerous other experts experts, it was just a matter of time before an exploit code for the now public DNS flaw would surface. An exploit code for the flaw allowing insertion of malicious DNS records into the cache of target nameservers has been posted to Metasploit, a free provider of information and tools on exploit techniques. According to reports Metasploit creator, H D Moore in collaboration with a researcher named “|)ruid” from Computer Academic Underground, created the exploit, dubbed “DNS BaliWicked Attack”, along with a DNS service created to assist with the exploit.

The following description has been provided for the exploit:

“This exploit targets a fairly ubiquitous flaw in DNS implementations which allow the insertion of malicious DNS records into the cache of the target nameserver. This exploit caches a single malicious host entry into the target nameserver. By causing the target nameserver to query for random hostnames at the target domain, the attacker can spoof a response to the target server including an answer for the query, an authority server record, and an additional record for that server, causing target nameserver to insert the additional record into the cache.”

However according to Moore the code has a limitation:

“This exploit can’t be used to overwrite an existing cache entry, so attackers will have a hard time spoofing common host names on busy DNS servers. The module added to Metasploit will display the expiration date for any pre-cached entries and automatically wait for that amount of time for completing the attack.”

Unfortunately a large number of organizations and ISPs are still unpatched and at risk. “In fact, of the 60 DNS servers I tested, more than half of them were still vulnerable,” says Neal Krawetz, owner of computer security consultancy Hacker Factor Solutions, in a blog post. “Considering that many of the ‘safe’ DNS servers were not vulnerable prior to this situation, this means that far fewer than half of the large ISPs have even reacted to the notice.”

Related Sources:
• http://www.caughq.org/exploits/CAU-EX-2008-0002.txt
• http://metasploit.com/.../dns/baliwicked_host.rb?rev=5579
• http://blogs.zdnet.com/security/?p=1545
• http://blog.wired.com/27bstroke6/2008/07/dns-exploit-in.html

Updates:
• |)ruid and HD Moore release part 2 of DNS exploit 7/24/2008 - ZDNet
• U.S. Computer Emergency Readiness Team (US-CERT) Acknowledges Publicly Available DNS Exploit 7/24/2008 - US-CERT