Asterisk is an open source private branch exchange and telephony toolkit. Prior to Asterisk 20.20.1, 21.12.3, 22.10.1, 23.4.1 and Certified Asterisk 20.7-cert11, 22.8-cert3, an authenticated attacker may cause a heap buffer overflow through an out-of-bounds write in the Codec2 decoder caused by a floor/ceil sample-count mismatch. The codec_codec2 module must be loaded and Codec2 must be configured on the attacked endpoint. The attacker must pass SIP authentication by username/password or source IP address matching, establish a call using Codec2, and send carefully crafted Codec2 audio packets. This issue is fixed in Asterisk 20.20.1, 21.12.3, 22.10.1, 23.4.1 and Certified Asterisk 20.7-cert11, 22.8-cert3.