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Cisco Admits Flaw in Networking Software
By Dennis Fisher
Cisco Systems Inc. has found a serious vulnerability that can be used to essentially disable virtually any device running the company's Internetwork Operating System software, including its ubiquitous routers and switches.
The vulnerability arises from IOS' failure to correctly handle a specific series of IPv4 packets sent to the device. When the sequence of packets hits the device, the IOS mistakenly flags the input queue on the network interface as being full. After a period of time, the device will stop processing traffic.
The device can be forced to stop routing any traffic on any interface and will require a complete restart to resume normal operation.
What makes this flaw even more serious is the fact that it can be exploited on such a large number of devices with very little effort. An attack could be targeted against a specific server, or could be launched randomly in an effort to cause a widespread denial-of-service.
Security experts at Internet Security Systems Inc. in Atlanta, who have been watching the situation, say there is a working exploit for this vulnerability but that it has not been released yet. ISS became aware of the vulnerability after noticing that a large number of the IP backbone operators were doing reboots of their networks. They asked around and found that Cisco had alerted the large network operators to the flaw and encouraged them to do emergency upgrades on their routers and switches.
This was basically a reboot of most of the Internet over the last 24 hours, said Chris Rouland, director of the X-Force research team at ISS. Most network operators take IOS upgrades very seriously and test them for weeks. This was pushed through in a couple of days, which gives you an idea of the scope of the problem.
This weakness affects versions 11 and 12 of IOS, up to 12.2. This represents the vast majority of Cisco's current product line, although products that run IPv6 are not vulnerable. Routers and switches made by Cisco, based in Mountain View, Calif., are among the most widely deployed devices on the Internet and handle a large portion of the traffic moving around the world.
Cisco has developed a free software upgrade that fixes the problem.
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