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Closing The RADIUS Security Gap

Since it was ratified in June, wireless administrators and vendors have hailed the IEEE 802.11i wireless security standard as the holy grail of secure wireless computing. However, wireless administrators were reminded last week that security standards aren't a replacement for implementing best practices.
Last week Aruba Wireless Networks brought to light a serious vulnerability related to how both wireless and wired networks access the RADIUS servers used by many enterprises for authentication. The insinuation was that the recently ratified IEEE 802.11i standard had an Achilles heel. This week the company offered a paper to the IETF's RADIUS Extensions Workgroup that describes in detail the vulnerability and how it might be exploited.

For its efforts, Aruba has been criticized by the press, other wireless vendors, and even wireless administrators for using this security flaw in a self-serving way to highlight their architecture. Whether or not that's true, this is a potentially significant issue that every enterprise that uses a RADIUS server should look into.

The RADIUS exploit that Aruba documented requires gaining access to a RADIUS packet exchange between the NAS (Network Access Server) and RADIUS server. The NAS for most traditional wireless networks is the access point " for those who use a wireless switch or appliance, it's usually the switch itself.

Because most RADIUS secrets are weak (simple words and/or 8 octet or shorter strings) and are hashed using MD5 (a one-way operation that transforms a string into a unique shorter, fixed-length value), they can be recovered relatively quickly offline using a dictionary attack. If a stronger secret with 8 octets was implemented, hackers will have to try all permutations, which means that key retrieval will take about 17 days, on average.

"RADIUS is more difficult to capture the hash (than LEAP), but slightly easier to crack," said Joshua Wright, co-author of the RFC (Request For Comments) and the researcher who implemented the 'asleap' attack on Cisco's LEAP security protocol. In the case of wireless traffic, the RADIUS secret can be used to eventually retrieve session encryption keys and reveal the plain-text version of the data communication.

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