In late 2023, a subtle but important security flaw, CVE-2023-5616, was found in Ubuntu’s GNOME Control Center—the graphical application that lets you adjust system settings. This bug specifically involved the SSH remote login status indicator, and it could leave your computer open to the internet without you realizing it, especially if you used a more modern setup for your SSH server.
Let’s break down what happened, how it affected users, and demonstrate with some code for better understanding.
What is CVE-2023-5616?
CVE-2023-5616 is a vulnerability in the gnome-control-center’s “Remote Login” setting under the “Sharing” panel on Ubuntu Linux. The tool is supposed to show you if remote access to your machine (via SSH) is ON or OFF, and lets you toggle it easily.
However, if the system was set to use systemd socket activation for the OpenSSH server (sshd), GNOME Control Center often got the status wrong. It could show “OFF” (SSH access is disabled), but the system was actually open and listening for SSH connections.
That means users could wrongly believe SSH remote login was disabled, when in fact, their system was accessible to anyone on the network or internet—potentially a big risk if you’re on a public or insecure network.
Older setups simply start sshd as a service at boot, and it keeps running
sudo systemctl enable ssh
sudo systemctl start ssh
But with systemd socket activation, sshd only starts up when a connection is attempted. A special socket listens for incoming requests. This can save system resources.
You might enable it like this
sudo systemctl stop ssh
sudo systemctl enable ssh.socket
sudo systemctl start ssh.socket
Now, *ssh.socket* is the listener, and *sshd* only launches when needed.
The Bug in gnome-control-center
GNOME Control Center checked only for the ssh.service status, not ssh.socket. So, if you had enabled SSH with *socket activation*, GNOME thought SSH was OFF, but in fact, remote login was possible.
Let’s verify the actual listening ports
sudo ss -tlnp | grep 22
Output should show port 22 is being watched by systemd, even though GNOME says SSH is “OFF”.
Configured socket-based SSH for efficiency or following a guide,
You were still at risk. Anyone who knew your IP or was on your network could try login attempts.
You might leave your device unattended, or travel with it, thinking it’s safe—when it really isn’t.
References and Fixes
- CVE-2023-5616 details (NVD)
- Ubuntu Security Notice USN-657-1
- GNOME Control Center bug report
The fix was to make GNOME Control Center check *both* ssh.service and ssh.socket before showing the status—so you get an accurate picture.
Ubuntu patched this in December 2023. Make sure you have the latest updates by running
sudo apt update && sudo apt upgrade
Exploit Details
This issue wasn’t about remote code execution or a classic “hack”—but about misleading information. The easiest “exploit” was that a local user, malware, or even a misconfigured script could enable SSH socket activation, and you’d never know from the GUI.
Conclusion
CVE-2023-5616 is a reminder that visual indicators in security GUIs must be accurate, especially for network-exposed features. Always double-check what your system says is enabled, and keep your software up to date.
If you want to dig deeper or ensure you’re safe, check out the original sources linked above!
Timeline
Published on: 04/15/2025 19:16:06 UTC
Last modified on: 04/16/2025 13:25:59 UTC