CVE-2023-49786 Explained : Impact and Mitigation

Asterisk is an open source private branch exchange and telephony toolkit vulnerable to Denial of Service via DTLS Hello packets during call initiation.

Understanding CVE-2023-49786

Asterisk prior to versions 18.20.1, 20.5.1, and 21.0.1, as well as certified-asterisk prior to 18.9-cert6, is susceptible to a DoS due to a race condition in the hello handshake phase of the DTLS protocol.

What is CVE-2023-49786?

Asterisk servers can face a massive Denial of Service attack due to a race condition in handling DTLS-SRTP for media setup, potentially denying new DTLS-SRTP encrypted calls during the attack.

The Impact of CVE-2023-49786

Abuse of this vulnerability may lead to a persistent Denial of Service on vulnerable Asterisk servers relying on DTLS-SRTP for calls.

Technical Details of CVE-2023-49786

The vulnerability is caused by a race condition in the hello handshake phase of the DTLS protocol, impacting Asterisk versions before the fixed versions mentioned.

Vulnerability Description

Asterisk is vulnerable to a DoS attack due to improper handling of DTLS Hello packets, affecting the availability of DTLS-SRTP encrypted calls.

Affected Systems and Versions

Versions < 18.20.1, 20.5.1, 21.0.1
Certified-asterisk < 18.9-cert6

Exploitation Mechanism

Attackers can exploit the race condition in the hello handshake phase of the DTLS protocol to disrupt DTLS-SRTP media setup.

Mitigation and Prevention

To address CVE-2023-49786, immediate actions and long-term security practices are crucial.

Immediate Steps to Take

Update Asterisk to versions 18.20.1, 20.5.1, 21.0.1, or 18.9-cert6 containing the fix.
Monitor and restrict network access to Asterisk servers.

Long-Term Security Practices

Regularly apply security patches and upgrades to Asterisk.
Conduct security assessments and audits to uncover potential vulnerabilities.

Patching and Updates

Ensure timely installation of security patches and updates to protect against known vulnerabilities.