The Asterisk Development Team reports:
It is possible for a user of the Asterisk Manager Interface to bypass a security check and execute shell commands when they should not have that ability. Sending the "Async" header with the "Application" header during an Originate action, allows authenticated manager users to execute shell commands. Only users with the "system" privilege should be able to do this. On systems that have the Asterisk Manager Interface, Skinny, SIP over TCP, or the built in HTTP server enabled, it is possible for an attacker to open as many connections to asterisk as he wishes. This will cause Asterisk to run out of available file descriptors and stop processing any new calls. Additionally, disk space can be exhausted as Asterisk logs failures to open new file descriptors.