DNS vulnerability ‘critical’
Fix available - at a price
Nominum Inc says a recently discovered flaw in the dominant domain name server on the internet is far more serious than originally thought, and could allow crackers to crash or even take control of any internet-connected application running on Unix,Kevin Murphy writes
"We know for sure we can use this bug to crash any application," said Richard Probst, VP of product management at Nominum, which has released a product that fixes the problem. "And we think we know how to use it to hijack any application, but we haven't seen an exploit yet."
The CERT Coordination Center, which tracks internet vulnerabilities for the US government, warned June 28 that a flaw in DNS resolver libraries (the code that handles the transformation of domain names into IP addresses) in multiple Unix applications were susceptible to a buffer overflow attack.
To exploit the attack, a cracker has to be in control of an authoritative name server for a domain (example.com). The server is set up to send a malformed response to DNS lookups. When an application running on Unix looks up a bad address in the cracker's domain, that application either crashes or is hijacked.
Because the malformed DNS responses actually look like healthy messages, they will also be stored on DNS caches, allowing the cracker to crash more applications even if the authoritative server is turned off.
CERT initially said companies that upgraded their DNS caching server to BIND 9, the latest version of the Berkeley Internet Name Domain name server, would be protected. However, it emerged August 27 that the only foolproof way to stop attacks is to upgrade your DNS resolver libraries, a fix Probst describes as "like a mini-Y2k response".
CERT said in its advisory: "The only complete solution to this problem is to upgrade to a corrected version of the DNS resolver libraries... Note that DNS resolver libraries can be used by multiple applications on most systems. It may be necessary to upgrade or apply multiple patches and then recompile statically linked applications."
The bug in question dates back to the 1980s, according to Probst, and still remains in most flavors of Unix, though Windows and Linux are unaffected. Products from IBM, Hewlett-Packard Co, Caldera International Inc (now SCO Group Inc), Network Appliance Inc and Nortel Networks Ltd are among those that use the vulnerable libraries. Most vendors have issued bulletins and patches.
Nominum says all the patching and recompiling makes securing your systems a logistical nightmare. One of its larger and more paranoid customers, which it would not name, demanded Nominum build a fix "as quickly as possible", and the company yesterday released into beta its first-ever commercial product, the DNS Response Validator.
DRV, a 1U appliance sits beside the DNS cache, inspects DNS messages for signs that they carry the malicious attack. If they do, it logs and blocks them. Probst said the device can create a "measurable but not problematic" performance issue (not enough to cause a bottleneck).
The product is available to beta customers now, for $30,000. Recognizing that some companies may just want a short-term solution while they patch and recompile their affected applications, Nominum said the DRV can also be leased for $1,500 a month.