CVE-2021-26717

Name: CVE-2021-26717
Creator: NVD / NIST
Published: 2021-02-18T20:15:12.667+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 2.18%

Last modified Jun 17, 2026

CVE-2021-26717 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 2.18% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

2.18%

80.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Digium	Asterisk	>= 16.0.0, < 16.16.1
Digium	Asterisk	>= 17.0.0, < 17.9.2
Digium	Asterisk	>= 18.0, < 18.2.1
Digium	Certified Asterisk	16.8

References

http://packetstormsecurity.com/files/161471/Asterisk-Project-Security-Advisory-AST-2021-002.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2021/Feb/58Mailing List, Patch, Third Party Advisory
https://downloads.asterisk.org/pub/security/Vendor Advisory
https://downloads.asterisk.org/pub/security/AST-2021-002.htmlVendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29203Issue Tracking, Patch, Vendor Advisory
http://packetstormsecurity.com/files/161471/Asterisk-Project-Security-Advisory-AST-2021-002.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2021/Feb/58Mailing List, Patch, Third Party Advisory
https://downloads.asterisk.org/pub/security/Vendor Advisory
https://downloads.asterisk.org/pub/security/AST-2021-002.htmlVendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29203Issue Tracking, Patch, Vendor Advisory

Timeline

Published: Feb 18, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26717?

How severe is CVE-2021-26717?

CVE-2021-26717 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 2.18% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26717?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-26717?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST