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Jumbo bug crashes Cisco anti-hacker appliances

I saw a peanut stand, heard a rubber band

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Security appliances from Cisco can crash when handling Jumbo Ethernet frames, the networking giant warned on Wednesday.

Cisco has published a software patch designed to address a denial of service vulnerability in its Intrusion Prevention System (IPS) appliances. IPS systems are designed to block common hacker attacks and exploits. But a bug in the devices meant that "kernel panic" leading to a crash might be induced when processing Jumbo Ethernet packets.

Recovery in these cases would involve resetting the devices using a power cycle. In the meantime network traffic would be cut off except in the case of Cisco's 4260 and 4270 IPS platforms, which have the option to allow traffic to bypass devices in the event of a system failure.

The flaw only applies where Cisco IPS platforms have Gigabit network interfaces installed and where these are deployed in inline mode. The flaw becomes a moot point in slower speed networks or where IPS devices are configured just to sniff traffic (promiscuous mode), where they essentially act as hi-tech burglar alarms.

Jumbo Ethernet is a data center technology designed to increase inter-server communication performance. By increasing the size of frames less effort is expending on unpacking packets in the same way it's easier to deal with one big envelope containing a wad of papers rather than a larger number of smaller letters. The technology, designed for hi-speed LANs, is not supported by default on Cisco routers or switches.

The vulnerability was reported to Cisco by HD Moore of Metasploit fame. There's no evidence that the flaw has been used in anger by hackers. Nonetheless sys admin would be prudent to patch vulnerable IPS systems, especially in the absence of any temporary fixes (workarounds).

The issue is explained in greater detail in Cisco's advisory here. ®

Bootnote

Jumbo Ethernet is so called in an analogy to elephants. Pop culture, going back to the classic Disney film Dumbo, would suggest elephants are scared witless by mice. Not so. Recent scientific research suggests that elephants are actually far more scared of honey bees, a trait that's been exploited in some farms in Africa to keep pachyderms away from crops by playing recordings of angry bees.

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