What’s Vulnerable › Vulnerabilities

CVE-2021-26717

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-02-18 · updated 2026-06-17

Description

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; from 17.0.0 before 17.9.2; from 18.0 before 18.2.1 — fixed in 16.16.1, 17.9.2, 18.2.1
• Digium Certified Asterisk: 16.8, 16.8-cert1-rc1, 16.8-cert1-rc2, 16.8-cert1-rc3, 16.8-cert1-rc4, 16.8-cert2 (+7)

How to fix

Upgrade to a fixed version: Digium Asterisk 16.16.1, 17.9.2, 18.2.1. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/161471/Asterisk-Project-Security-Advisory-AST-2021-002.html
• http://seclists.org/fulldisclosure/2021/Feb/58
• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-002.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29203
• http://packetstormsecurity.com/files/161471/Asterisk-Project-Security-Advisory-AST-2021-002.html
• http://seclists.org/fulldisclosure/2021/Feb/58
• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-002.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29203

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