Multiple Sniffer Vendor DNS Decode Vulnerability

A vulnerability exists in the DNS decode capabilities provided as part of the tcpdump sniffer, from LBL, as well as other sniffers, including Ethereal, by Gerald Combs. These sniffers will attempt to decode DNS request and queries. However, due to the DNS name compression scheme, it is possible to create a DNS packet such that tcpdump will be caught in an infinite loop, while trying to decompress. This will prevent the sniffer from displaying further packets. If tcpdump is being used as some part of and intrusion detection system, this could allow an intruder to evade this system.

When tcpdump is logging to a file, it is not affected by this vulnerability. Upon reading from a file which contains recorded packets, it will enter an infinite loop when it encounters packets of this type.


 

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