CVE-2021-26906

Name: CVE-2021-26906
Creator: NVD / NIST
Published: 2021-02-18T20:15:12.743+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 2.55%

Last modified Jun 17, 2026

CVE-2021-26906 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. An issue was discovered in res_pjsip_session.c in Digium Asterisk through 13.38.1; 14.x, 15.x, and 16.x through 16.16.0; 17.x through 17.9.1; and 18.x through 18.2.0, and Certified Asterisk through 16.8-cert5. An SDP negotiation vulnerability in PJSIP allows a remote server to potentially crash Asterisk by sending specific SIP responses that cause an SDP negotiation failure.. EPSS estimates a 2.55% chance of exploitation in the next 30 days.

Description

An issue was discovered in res_pjsip_session.c in Digium Asterisk through 13.38.1; 14.x, 15.x, and 16.x through 16.16.0; 17.x through 17.9.1; and 18.x through 18.2.0, and Certified Asterisk through 16.8-cert5. An SDP negotiation vulnerability in PJSIP allows a remote server to potentially crash Asterisk by sending specific SIP responses that cause an SDP negotiation failure.

Metrics

CVSS 3.1

5.9/10

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

EPSS Probability

2.55%

83.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-404

Affected Software

Vendor	Product	Versions
Digium	Asterisk	>= 13.0.0, < 13.38.2
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/161477/Asterisk-Project-Security-Advisory-AST-2021-005.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2021/Feb/61Mailing List, Patch, Third Party Advisory
https://downloads.asterisk.org/pub/security/Vendor Advisory
https://downloads.asterisk.org/pub/security/AST-2021-005.htmlVendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29196Issue Tracking, Patch, Vendor Advisory
http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2021/Feb/61Mailing List, Patch, Third Party Advisory
https://downloads.asterisk.org/pub/security/Vendor Advisory
https://downloads.asterisk.org/pub/security/AST-2021-005.htmlVendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29196Issue Tracking, Patch, Vendor Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2021-26906?

How severe is CVE-2021-26906?

CVE-2021-26906 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 2.55% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26906?

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-2021-26906?

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

Scan your code now

Source: NVD / NIST