CVE-2020-28327: A res_pjsip_session crash was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1....

Description

A res_pjsip_session crash was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1. and Certified Asterisk before 16.8-cert5. Upon receiving a new SIP Invite, Asterisk did not return the created dialog locked or referenced. This caused a gap between the creation of the dialog object, and its next use by the thread that created it. Depending on some off-nominal circumstances and timing, it was possible for another thread to free said dialog in this gap. Asterisk could then crash when the dialog object, or any of its dependent objects, were dereferenced or accessed next by the initial-creation thread. Note, however, that this crash can only occur when using a connection-oriented protocol (e.g., TCP or TLS, but not UDP) for SIP transport. Also, the remote client must be authenticated, or Asterisk must be configured for anonymous calling.

Metrics

CVSS 3.1

5.3/10

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

EPSS Probability

1.97%

77.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-404

Affected Software

Vendor	Product	Versions
Digium	Certified Asterisk	16.8
Sangoma	Asterisk	>= 13.0.0, < 13.37.1
Sangoma	Asterisk	>= 16.0.0, < 16.14.1
Sangoma	Asterisk	>= 17.0.0, < 17.8.1
Sangoma	Asterisk	>= 18.0.0, < 18.0.1

References

http://downloads.asterisk.org/pub/security/AST-2020-001.htmlPatch, Vendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29057Exploit, Issue Tracking, Vendor Advisory
http://downloads.asterisk.org/pub/security/AST-2020-001.htmlPatch, Vendor Advisory
https://issues.asterisk.org/jira/browse/ASTERISK-29057Exploit, Issue Tracking, Vendor Advisory

Timeline

Published: Nov 6, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-28327?

A res_pjsip_session crash was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1. and Certified Asterisk before 16.8-cert5. Upon receiving a new SIP Invite, Asterisk did not return the created dialog locked or referenced. This caused a gap between the creation of the dialog object, and its next use by the thread that created it. Depending on some off-nominal circumstances and timing, it was possible for another thread to free said dialog in this gap. Asterisk could then crash when the dialog object, or any of its dependent objects, were dereferenced or accessed next by the initial-creation thread. Note, however, that this crash can only occur when using a connection-oriented protocol (e.g., TCP or TLS, but not UDP) for SIP transport. Also, the remote client must be authenticated, or Asterisk must be configured for anonymous calling.

How severe is CVE-2020-28327?

CVE-2020-28327 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 1.97% probability of exploitation in the next 30 days.

How do I fix CVE-2020-28327?

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.