Asterisk maintains an internal cache for devices. The device state cache holds the state of each device known to Asterisk, such that consumers of device state information can query for the last known state for a particular device, even if it is not part of an active call. The concept of a device in Asterisk can include things that do not have a physical representation. One way that this currently occurs is when anonymous calls are allowed in Asterisk. A device is automatically created and stored in the cache for each anonymous call that occurs; this is possible in the SIP and IAX2 channel drivers and through channel drivers that utilize the res_jabber/res_xmpp resource modules (Gtalk, Jingle, and Motif). Attackers exploiting this vulnerability can attack an Asterisk system configured to allow anonymous calls by varying the source of the anonymous call, continually adding devices to the device state cache and consuming a system's resources.
Related bug tracker: https://issues.asterisk.org/jira/browse/ASTERISK-20175
Thanks for taking the time to report this bug and helping to make Ubuntu better. Since the package referred to in this bug is in universe or multiverse, it is community maintained. If you are able, I suggest coordinating with upstream and posting a debdiff for this issue. When a debdiff is available, members of the security team will review it and publish the package. See the following link for more information: https:/