In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.

In Contiki 3.0, a buffer overflow in the Telnet service allows remote attackers to cause a denial of service because the ls command is mishandled when a directory has many files with long names.

In Contiki 3.0, a Telnet server that silently quits (before disconnection with clients) leads to connected clients entering an infinite loop and waiting forever, which may cause excessive CPU consumption.

In Contiki 3.0, potential nonterminating acknowledgment loops exist in the Telnet service. When the negotiated options are already disabled, servers still respond to DONT and WONT requests with WONT or DONT commands, which may lead to infinite acknowledgment loops, denial of service, and excessive CPU consumption.