| From the CVE entries:
chan_sip.c in the SIP channel driver in Asterisk Open Source 1.4.x before 1.4.41.2, 1.6.2.x before 1.6.2.18.2, and 1.8.x before 1.8.4.4, and Asterisk Business Edition C.3.x before C.3.7.3, disregards the "alwaysauthreject' option and generates different responses for invalid SIP requests depending on whether the user account exists, which allows remote attackers to enumerate account names via a series of requests. (CVE-2011-2536)
reqresp_parser.c in the SIP channel driver in Asterisk Open Source 1.8.x before 1.8.4.3 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a SIP packet with a Contact header that lacks a < (less than) character. (CVE-2011-2665)
The default configuration of the SIP channel driver in Asterisk Open Source 1.4.x through 1.4.41.2 and 1.6.2.x through 1.6.2.18.2 does not enable the "alwaysauthreject" option, which allows remote attackers to enumerate account names by making a series of invalid SIP requests and observing the differences in the responses for different usernames, a different vulnerability than CVE-2011-2536. (CVE-2011-2666)
chan_sip.c in the SIP channel driver in Asterisk Open Source 1.8.x before 1.8.7.1 and 10.x before 10.0.0-rc1 does not properly initialize variables during request parsing, which allows remote authenticated users to cause a denial of service (daemon crash) via a malformed request. (CVE-2011-4063) | 