What’s Vulnerable › Vulnerabilities

CVE-2023-49786: Asterisk susceptible to Denial of Service via DTLS Hello packets during call initiation

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 5.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-12-14 · updated 2026-06-17
• Weakness: CWE-703

Description

Asterisk is an open source private branch exchange and telephony toolkit. In Asterisk prior to versions 18.20.1, 20.5.1, and 21.0.1; as well as certified-asterisk prior to 18.9-cert6; Asterisk is susceptible to a DoS due to a race condition in the hello handshake phase of the DTLS protocol when handling DTLS-SRTP for media setup. This attack can be done continuously, thus denying new DTLS-SRTP encrypted calls during the attack. Abuse of this vulnerability may lead to a massive Denial of Service on vulnerable Asterisk servers for calls that rely on DTLS-SRTP. Commit d7d7764cb07c8a1872804321302ef93bf62cba05 contains a fix, which is part of versions 18.20.1, 20.5.1, 21.0.1, amd 18.9-cert6.

Affected products

• Digium Asterisk: before 18.20.1; from 19.0.0 before 20.5.1; 21.0.0 — fixed in 18.20.1, 20.5.1
• Sangoma Certified Asterisk: 13.13.0, 13.13.0-cert1, 13.13.0-cert1-rc1, 13.13.0-cert1-rc2, 13.13.0-cert1-rc3, 13.13.0-cert1-rc4 (+22)

How to fix

Upgrade to a fixed version: Digium Asterisk 18.20.1, 20.5.1. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/176251/Asterisk-20.1.0-Denial-Of-Service.html
• http://seclists.org/fulldisclosure/2023/Dec/24
• http://www.openwall.com/lists/oss-security/2023/12/15/7
• https://github.com/EnableSecurity/advisories/tree/master/ES2023-01-asterisk-dtls-hello-race
• https://github.com/asterisk/asterisk/commit/d7d7764cb07c8a1872804321302ef93bf62cba05
• https://github.com/asterisk/asterisk/security/advisories/GHSA-hxj9-xwr8-w8pq
• https://lists.debian.org/debian-lts-announce/2023/12/msg00019.html
• http://packetstormsecurity.com/files/176251/Asterisk-20.1.0-Denial-Of-Service.html
• http://seclists.org/fulldisclosure/2023/Dec/24
• http://www.openwall.com/lists/oss-security/2023/12/15/7
• https://github.com/EnableSecurity/advisories/tree/master/ES2023-01-asterisk-dtls-hello-race
• https://github.com/asterisk/asterisk/commit/d7d7764cb07c8a1872804321302ef93bf62cba05

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