Denial-of-Service Flaw Found in DNS Protocol

A security flaw in the ubiquitous Domain Name System protocol could cause widespread DoS attacks; Cisco issues patches.

A high-profile security research outfit on Tuesday warned that a newly discovered flaw in the Domain Name System protocol could be exploited remotely to crash vulnerable servers.

The vulnerability, which carries a "moderate risk" rating, was flagged by the U.K.-based National Infrastructure Security Co-ordination Centre.

In a public advisory, the NISCC said the flaw exists in the recursion process used by some DNS implementations to decompress compressed DNS messages. "Under certain circumstances, it is possible to cause the DNS server to terminate abnormally," the Center said.

The DNS protocol, which handles the translation of domain names into IP addresses, is considered one of the Internets most vital service and security-related hiccups can potentially be very disruptive.

However, in this case, the overall risk is minimized because the Internet Systems Consortiums BIND (Berkeley Internet Name Domain) is not considered vulnerable. BIND versions 8 and 9 are the most commonly used DNS servers on the Internet, especially on Unix-like systems, where it is a de facto standard.

Mike Poor, founder and senior security analyst at Intelguardians Network Intelligence LLC, downplayed the overall severity of the flaw but recommended patches for vulnerable DNS implementations.

"At this point its a denial-of-service issue. If this vulnerability is found to be more widespread then currently thought, it could lead to outages if exploited," Poor told Ziff Davis Internet News.

According to the NISCC advisory, Microsoft Corp. provided the following response to the warning: "We have conducted an investigation of the issue you had reported. At this point, we have determined that the MS implementation of DNS is not affected."

/zimages/2/28571.gifClick here to read about how the rise in phishing attacks is driving interest in technology to lock down the DNS.

At least one affected vendor, Cisco Systems Inc., has already released patches for multiple product lines.

Cisco posted an online advisory to warn that the bug could be exploited to crash some of its devices.

Affected products include Cisco IP Phones 7902/7905/7912; Cisco ATA (Analog Telephone Adaptor) 186/188; and several Cisco Unity Express Cisco ACNS (Application and Content Networking System) devices.

Information on affected software versions and appropriate fixes can be found here.

Juniper Networks Inc. and NEC Corp. said their products were not affected.

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