What’s Vulnerable › Vulnerabilities

CVE-2021-26906

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-02-18 · updated 2026-06-17
• Weakness: CWE-404

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.

Affected products

• Digium Asterisk: from 13.0.0 before 13.38.2; 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 13.38.2, 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 13.38.2, 16.16.1, 17.9.2, 18.2.1. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.html
• http://seclists.org/fulldisclosure/2021/Feb/61
• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-005.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29196
• http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.html
• http://seclists.org/fulldisclosure/2021/Feb/61
• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-005.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29196

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