A vulnerability in the way Apple iChat handles specially crafted TXT key hashes could lead to denial of service.
Apple iChat is an instant message client for Apple Mac OS X. Apple iChat Agent is a back-end process that manages iChat sessions and available contacts. Apple Bounjour is a service provided with Apple Mac OS X that facilitates automatic discovery of computers, devices, and services on IP networks. The iChat Agent uses Bonjour to discover available contacts. The Apple iChat Agent contains a vulnerability that could be exploited when it attempts to handle specially crafted TXT key hashes received via Bonjour messages. According to MOAB-29-01-2007:
This will instantly cause a SIGTRAP signal to be sent to the process, causing a so-called 'crash'. Further attempts to launch iChat Bonjour functionality again will fail as mDNSResponder keeps the crafted record (and restarting it will be necessary).
A remote, unauthenticated attacker on the same multicast network may be able to cause iChat to crash, thereby creating a denial-of-service condition.