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 out-of-bounds write in "chan_unistim" "DIALPAGE" digit handling can overflow the "phone_number" field and crash Asterisk when an attacker sends a carefully crafted incoming request packet. The "chan_unistim" module must be loaded and configured with a valid "UNISTIM UDP port" that the attacker can reach. The attacker must register as a configured "phone MAC", or the deployment must have an equivalent "production/autoprovisioning" path that allows the client to reach the main page. 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.