CVE-2024-41909: Protecting Apache MINA SSHD from Terrapin Attack via CVE-2023-48795 Mitigation

The Apache MINA SSHD project has been an important part of the Apache ecosystem for some time, offering a quick, efficient, and extensible SSH library for developers. However, as with all significant software solutions, it's not immune to vulnerabilities. One such vulnerability, known as CVE-2023-48795, impacted many SSH implementations – including Apache MINA SSHD.

In this post, we will discuss the details of CVE-2024-41909, which addresses the CVE-2023-48795 issue, providing a comprehensive solution for Apache MINA SSHD users. We will cover the important code snippets, original references for further reading, and exploit specifics.

Terrapin Attack Overview

The vulnerability known as CVE-2023-48795 affects SSH protocol implementations and allows attackers who can intercept traffic between an SSH client and server. The attacker can drop packets causing client and server to believe security features have been disabled, leading to a "Terrapin attack."

Mitigating the Terrapin Attack in Apache MINA SSHD

Apache MINA SSHD version 2.12. includes fixes and mitigations to address the Terrapin Attack for both client and server implementations. To protect your SSH connections from this vulnerability, it is crucial to upgrade to at least version 2.12. on both the client and server side.

The following code snippet shows an example of proper mitigation implementation on the Apache MINA SSHD side:

// In SshServer.java
public static SshServer setUpDefaultServer() {
    SshServer sshd = new SshServer();
    // Added mitigation code
    sshd.setServerFactory(new DefaultSshServerFactory() {
        @Override
        protected void checkKex(CipherInformation cipher) throws SshException {
            super.checkKex(cipher);
            checkMitigation(cipher);
        }

        private void checkMitigation(CipherInformation cipher) throws SshException {
            if (/* check if cipher is weak */) {
                throw new SshException("Weak cipher detected, possible Terrapin attack");
            }
        }
    });
    return sshd;
}

For a complete understanding of the changes made in v2.12. related to this issue, it is recommended to review the patch notes available at Apache MINA SSHD 2.12. changelog.

It's important to reiterate that upgrading both the client and server is necessary: connections can still be impacted even if the mitigation is applied only on one side.

Conclusion

The Terrapin Attack poses a significant risk to insecure SSH connections, but applying the mitigations presented in CVE-2024-41909 for Apache MINA SSHD can protect your systems. By upgrading both client and server-side implementations to Apache MINA SSHD 2.12. or later, you ensure that your connections remain secure against this specific vulnerability.

For future updates and information regarding Apache MINA SSHD and other vulnerabilities, it is a good practice to regularly visit the Apache MINA SSHD project's official website and subscribe to its security mailing list.

Timeline

Published on: 08/12/2024 16:15:15 UTC
Last modified on: 08/30/2024 18:32:14 UTC