CVE-2023-41378: Exploring the Calico Typha Vulnerability - Denial of Service Through TLS Handshake Blocking

In recent cybersecurity news, a vulnerability called CVE-2023-41378 has emerged in Calico Typha's server that could potentially lead to a denial of service attack. Before diving into the details of this vulnerability, let's briefly understand what Calico Typha is and its role in a Kubernetes environment.

Calico Typha is a component of Project Calico, which is an open-source networking and network security solution for containers, virtual machines, and native host-based workloads. Calico Typha is primarily used to reduce the load on the Kubernetes API server by acting as a fan-out proxy for watchers of Kubernetes resources.

Vulnerability Details

The root cause of this vulnerability lies in the way Calico Typha server handles TLS handshakes for incoming client connections. A client TLS handshake, when not handled correctly or performed maliciously, can block the server indefinitely, causing a denial of service. This is mainly because the TLS Handshake() call is performed within the main server handle loop without any timeout. As a result, other connections remain idle, waiting for the problematic handshake to complete.

The vulnerable code snippet is as follows

// ... other code ...

for {
    conn, err := tlsListener.Accept()
    if err != nil {
        // ... error handling ...
    }

    go func() {
        // ... other code ...

        // Vulnerable code: TLS Handshake performed inside the main server loop without timeout
        tlsConn, err := conn.(*tls.Conn).Handshake()
        if err != nil {
            // ... error handling ...
        }

        // ... other code ...
    }()
}

// ... other code ...

Mitigation

To mitigate this vulnerability, it is important to include timeouts for the TLS Handshake process. The updated code snippet should look like this:

// ... other code ...

for {
    conn, err := tlsListener.Accept()
    if err != nil {
        // ... error handling ...
    }

    go func() {
        // ... other code ...

        // Fixed code: TLS Handshake with a timeout
        tlsConn := conn.(*tls.Conn)
        errCh := make(chan error, 1)
        go func() {
            errCh <- tlsConn.Handshake()
        }()

        select {
        case err := <-errCh:
            if err != nil {
                // ... error handling ...
            }
        case <-time.After(time.Duration(TLSHandshakeTimeout) * time.Second):
            // ... handle the timeout situation ...
        }

        // ... other code ...
    }()
}

// ... other code ...

The code above adds a timeout for the TLS Handshake, preventing the Calico Typha server from getting stuck indefinitely and causing a denial of service.

For further details about this vulnerability, please follow these links

1. Calico Typha Repository on GitHub
2. Project Calico Documentation

Conclusion

In this post, we have discussed the CVE-2023-41378 vulnerability in Calico Typha, which can potentially be exploited to launch a denial of service attack by blocking the server indefinitely. By implementing a timeout for the TLS Handshake process, you can mitigate this vulnerability and ensure your Calico Typha server remains stable and secure.

Timeline

Published on: 11/06/2023 16:15:42 UTC
Last modified on: 11/14/2023 17:48:01 UTC