nessus plugin id 41028.

3 min read 24-02-2025

Nessus plugin ID 41028 flags the use of weak or outdated SSH cipher suites on a target system. This vulnerability significantly weakens the security of your SSH connections, making them susceptible to various attacks, including man-in-the-middle (MITM) attacks. This article will delve into the details of this plugin, explaining its implications and outlining effective mitigation strategies.

What is SSH and Why are Weak Ciphers a Problem?

SSH (Secure Shell) is a cryptographic network protocol that provides a secure channel over an unsecured network. It's widely used for remote server administration, secure file transfers, and other sensitive network operations. The security of SSH relies heavily on the cipher suites it employs for encryption and authentication.

Weak SSH ciphers, like those identified by Nessus plugin 41028, are vulnerable to cryptanalysis techniques. Modern computing power can crack these older ciphers relatively easily, compromising the confidentiality and integrity of data transmitted over the SSH connection. An attacker exploiting this vulnerability could intercept sensitive information, manipulate data in transit, or even take control of the target system.

Understanding Nessus Plugin ID 41028

Nessus plugin ID 41028 specifically detects the presence of weak or deprecated SSH cipher suites. This means the target system is using encryption algorithms that are considered insecure by current standards. The plugin highlights the vulnerable ciphers and provides recommendations for remediation. The severity is typically high, reflecting the potential impact of a successful exploit.

What Ciphers Does it Detect?

The exact ciphers flagged by this plugin may vary depending on the Nessus version and the target system's configuration. However, it commonly detects ciphers like:

DES (Data Encryption Standard): An extremely outdated and easily broken encryption algorithm.
3DES (Triple DES): While an improvement over DES, it's still considered weak by modern standards.
RC4 (Rivest Cipher 4): Known to have significant vulnerabilities and is widely deprecated.
Other outdated or insecure algorithms: The plugin checks against a regularly updated list of known weak ciphers.

Mitigating the Risk: Steps to Take

Addressing the vulnerability flagged by Nessus plugin ID 41028 involves updating the SSH server configuration to utilize strong, modern cipher suites. The specific steps will vary slightly depending on the operating system (Linux, Windows, etc.), but the general process is as follows:

1. Identify the Vulnerable System(s)

Use Nessus or another vulnerability scanner to identify all systems affected by this plugin. Accurate identification is crucial for effective remediation.

2. Access SSH Server Configuration

The location of the SSH configuration file varies by operating system:

Linux (Debian/Ubuntu): /etc/ssh/sshd_config
Linux (Red Hat/CentOS): /etc/ssh/sshd_config
Windows (OpenSSH): The configuration is typically managed through the Windows services interface.

3. Update SSH Cipher Suites

Modify the sshd_config file (or equivalent) to specify strong cipher suites. You should not simply remove weak ciphers; you must explicitly specify strong alternatives. Here's an example of a robust configuration for sshd_config:

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,[email protected]
MACs hmac-sha2-256,hmac-sha2-512
KexAlgorithms curve25519-sha256,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256

Remember to replace these with the ciphers supported by your specific SSH server version and client. Consult the OpenSSH documentation for the most up-to-date list of recommended ciphers.

4. Restart SSH Service

After making changes to the configuration file, restart the SSH service to apply the new settings. This command varies depending on the OS. For example, on most Linux distributions you would use: sudo systemctl restart ssh

5. Verify the Changes

Re-run the Nessus scan to confirm that the weak ciphers have been successfully removed and replaced with strong alternatives. The plugin should no longer report the vulnerability.

Proactive Measures and Best Practices

Beyond immediate remediation, proactive security measures are crucial:

Regular Security Audits: Conduct regular vulnerability scans using tools like Nessus to proactively identify and address security weaknesses.
Keep Software Updated: Maintain your SSH server software and operating systems up-to-date to benefit from security patches and improved cipher suite support.
Principle of Least Privilege: Restrict SSH access to only authorized users and grant only the necessary permissions.
Strong Passwords/Keys: Use strong passwords or SSH keys for authentication, avoiding easily guessable credentials.

By understanding the implications of Nessus plugin ID 41028 and following the mitigation steps, you can significantly strengthen the security of your SSH connections and protect your systems from potential attacks. Remember that maintaining up-to-date security practices is a continuous process.