chan_sip in Asterisk Open Source 1.8.x 11.x before 11.21.1 12.x and 13.x before 13.7.1 and Certified Asterisk 1.8.28 11.6 before 11.6-cert12 and 13.1 before 13.1-cert3 when the timert1 sip.conf configuration is set to a value greater than 1245 allows remote attackers to cause a denial of service (file descriptor consumption) via vectors related to large retransmit timeout values.