Understanding OpenSSH Versioning on Ubuntu

When reviewing a penetration test or security report, you may see a warning regarding your server’s OpenSSH version. These tools typically flag any version that doesn’t match the most recent upstream release as a vulnerability.

However, a lower version number doesn’t necessarily mean that your SpinupWP server is insecure. This is because Ubuntu handles security updates differently than other distributions, ensuring that known vulnerabilities are patched while maintaining the stability of your server’s configuration.

How Ubuntu Manages Security Patches

Ubuntu utilizes a process called backporting to maintain the security of its packages. When a new vulnerability (CVE) is discovered, the Ubuntu security team typically does not upgrade the entire OpenSSH package to the latest version, as upgrading to a new major version could introduce breaking changes.

Instead, the security team “backports” the specific fix. They take the patch from the newest version of OpenSSH and apply it to the stable version already running on your release of Ubuntu. This ensures your server stays protected against the latest threats while maintaining the stability required for a production environment.

Understanding OpenSSH Version String

You can check which version of OpenSSH you are currently running by connecting to your server via SSH and running the following command:

ssh -V

The output will look similar to this:

OpenSSH_9.6p1 Ubuntu-3ubuntu13.15, OpenSSL 3.0.13 30 Jan 2024

In this example, 9.6p1 is the base version of OpenSSH that originally shipped with Ubuntu 24.04 LTS. However, the most important part for security audits lies in the suffix: 3ubuntu13.15.

This suffix indicates that this is the 15th update released by Ubuntu for this specific package. While the base version number remains the same to ensure compatibility, the software itself already includes the latest security patches released by Ubuntu addressing the latest vulnerabilities.

OpenSSH Versions per Ubuntu Release

The following table lists the base OpenSSH versions for each Ubuntu LTS release. If your server’s OpenSSH base version matches the one listed for your OS, it is up to date and protected by Ubuntu’s backported security patches.

Limitations of Automated Scanning

Many security scanners rely on a technique known as banner grabbing. The tool requests the version string from the server, identifies a version number like 9.6p1, and compares it against a database of known vulnerabilities for that specific release.

Because these automated tools often do not account for the Ubuntu-specific suffix (e.g., 3ubuntu13.15), they may flag the service as vulnerable simply because it does not match the latest “upstream” version (such as 10.2). In these cases, the scanner is merely reporting a version mismatch rather than an active, unpatched vulnerability.

Verifying a Specific CVE

If a security report flags a specific CVE (Common Vulnerabilities and Exposures) ID, you can verify if the fix has been applied to your server directly from the command line. For example, to check for a specific vulnerability, run:

sudo apt-get changelog openssh-server | grep -i "CVE-YYYY-XXXX"

Replace CVE-YYYY-XXXX with the ID from your report. If the patch has been applied, it will appear in the package’s changelog. You can also search for any CVE on the official Ubuntu Security Tracker to see its status for your specific Ubuntu release.

Keeping Your Server Updated

As long as you are keeping your server packages up to date, you don’t need to worry about manual OpenSSH upgrades. SpinupWP simplifies this by ensuring your server is configured to receive these security updates automatically.

You can also manually ensure that you have the latest patches by running:

sudo apt update && sudo apt upgrade

If a critical security patch is applied to OpenSSH, the service typically needs to be restarted for the changes to take effect:

sudo systemctl restart ssh.service