CVE-2021-26717: Digium Asterisk

High severity, CVSS 7.5. EPSS: 2.2% chance of exploitation in the next 30 days.

An issue was discovered in Sangoma Asterisk 16.x before 16.16.1, 17.x before 17.9.2, and 18.x before 18.2.1 and Certified Asterisk before 16.8-cert6. When re-negotiating for T.38, if the initial remote response was delayed just enough, Asterisk would send both audio and T.38 in the SDP. If this happened, and the remote responded with a declined T.38 stream, then Asterisk would crash.

Affected products

• Digium Asterisk: from 16.0.0, before 16.16.1 (fixed in 16.16.1); from 17.0.0, before 17.9.2 (fixed in 17.9.2); from 18.0, before 18.2.1 (fixed in 18.2.1)
• Digium Certified Asterisk: version 16.8 only

Published 2021-02-18. Last modified 2026-06-17.