CVE-2020-24659 : Exploit Details and Defense Strategies

An issue was discovered in GnuTLS before 3.6.15 where a server can trigger a NULL pointer dereference in a TLS 1.3 client, leading to a crash in the application's error handling path.

Understanding CVE-2020-24659

This CVE describes a vulnerability in GnuTLS that could be exploited by a malicious server to cause a denial of service (DoS) by triggering a NULL pointer dereference in a TLS 1.3 client.

What is CVE-2020-24659?

GnuTLS before version 3.6.15 is affected by a vulnerability that allows a server to crash a TLS 1.3 client by sending a no_renegotiation alert with unexpected timing, followed by an invalid second handshake. This results in a NULL pointer dereference in the client's error handling path.

The Impact of CVE-2020-24659

The vulnerability can be exploited by a remote attacker to crash a TLS 1.3 client, leading to a denial of service condition. This could potentially disrupt critical services relying on GnuTLS for secure communication.

Technical Details of CVE-2020-24659

GnuTLS Vulnerability

Vulnerability Description

A NULL pointer dereference can be triggered in a TLS 1.3 client due to unexpected timing of a no_renegotiation alert and an invalid second handshake, leading to a crash in the error handling path.

Affected Systems and Versions

GnuTLS versions before 3.6.15 are affected by this vulnerability.

Exploitation Mechanism

A malicious server sends a no_renegotiation alert with unexpected timing, followed by an invalid second handshake, causing a NULL pointer dereference in the client's error handling path.

Mitigation and Prevention

Protecting Against CVE-2020-24659

Immediate Steps to Take

Update GnuTLS to version 3.6.15 or later to mitigate the vulnerability.
Monitor vendor advisories and apply patches promptly.

Long-Term Security Practices

Regularly update software and libraries to the latest versions.
Implement network security measures to detect and block malicious traffic.

Patching and Updates

Apply security patches provided by GnuTLS promptly to address this vulnerability.