What’s Vulnerable › Vulnerabilities

CVE-2021-26713

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-02-19 · updated 2026-06-17
• Weakness: CWE-787

Description

A stack-based buffer overflow in res_rtp_asterisk.c in Sangoma Asterisk before 16.16.1, 17.x before 17.9.2, and 18.x before 18.2.1 and Certified Asterisk before 16.8-cert6 allows an authenticated WebRTC client to cause an Asterisk crash by sending multiple hold/unhold requests in quick succession. This is caused by a signedness comparison mismatch.

Affected products

• Digium Asterisk: from 16.0.0 before 16.16.1; from 17.0.0 before 17.9.2; from 18.0.0 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

• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-004.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29205
• https://downloads.asterisk.org/pub/security/
• https://downloads.asterisk.org/pub/security/AST-2021-004.html
• https://issues.asterisk.org/jira/browse/ASTERISK-29205

Get alerted when CVE-2021-26713 or the next vulnerability affects your stack