Major New DNS Vulnerability Discovered

The Internet Systems Consortium has issued a warning that certain versions of BIND are vulnerable to a denial of service attack. BIND is the most widely used domain name system protocol implementation. The latest version of BIND, 9.7.3, is not affected, but versions 9.7.1 through 9.7.2-P3 are vulnerable. Attackers could exploit the vulnerability to create a denial of service attack because of the way that BIND handles incremental zone transfers (IXFR), which is a technique for transferring data on top of the Transmission Control Protocol (TCP).

"When an authoritative server processes a successful IXFR transfer or a dynamic update, there is a small window of time during which the IXFR/update--coupled with a query--may cause a deadlock to occur," according to the ISC's security advisory issued on Tuesday. "This deadlock will cause the server to stop processing all requests. A high query rate and/or a high update rate will increase the probability of this condition." According to the ISC, this severe vulnerability can be remotely exploited, although no related attacks have been seen in the wild.

DNS is the technique used to resolve domain names into IP addresses. Accordingly, security experts are urging any organizations running a vulnerable version of BIND to upgrade immediately. "IXFRs between authoritative name servers are a vital part of keeping DNS both alive and correct," said Paul Ducklin head of technology for antivirus firm Sophos in the Asia-Pacific region, in a blog post.

With 300,000 new computers being connected to the Internet every day, as well as the role of DNS in supporting cloud computing, its importance continues to increase. "DNS servers are at the heart of many cloud-style security services, providing the mechanism by which up-to-date blocklist data is published," said Ducklin. He also noted that Apple OS X includes a copy of BIND, though most people don't run it. Even if they do, however, the latest Mac operating system, OS X 10.6.6, includes the older BIND 9.6, which is not vulnerable to the above exploit. "Sometimes, being behind the curve is a good thing," he said.

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