CVE-2021-37706: Asterisk Certified Asterisk

Critical severity, CVSS 9.8. EPSS: 4.6% chance of exploitation in the next 30 days.

PJSIP is a free and open source multimedia communication library written in C language implementing standard based protocols such as SIP, SDP, RTP, STUN, TURN, and ICE. In affected versions if the incoming STUN message contains an ERROR-CODE attribute, the header length is not checked before performing a subtraction operation, potentially resulting in an integer underflow scenario. This issue affects all users that use STUN. A malicious actor located within the victim’s network may forge and send a specially crafted UDP (STUN) message that could remotely execute arbitrary code on the victim’s machine. Users are advised to upgrade as soon as possible. There are no known workarounds.

Affected products

• Asterisk Certified Asterisk: before 16.8.0 (fixed in 16.8.0); version 16.8.0 only
• Debian Debian Linux: version 9.0 only; version 10.0 only
• Sangoma Asterisk: from 16.0.0, before 16.24.1 (fixed in 16.24.1); from 18.0.0, before 18.10.1 (fixed in 18.10.1); from 19.0.0, before 19.2.1 (fixed in 19.2.1)
• Teluu Pjsip: up to and including 2.11.1

Published 2021-12-22. Last modified 2026-06-17.