Have you ever spun up a blazing fast virtual machine instance on Google Cloud Platform, logged in via default SSH, and thought – this seems almost too easy?
Well, in some ways it is. The convenience of services like Compute Engine also introduce security considerations. But with just a bit of added effort, we can reap the benefits while avoiding the pitfalls!
In this comprehensive guide, you‘ll learn:
- Key background on SSH and port fundamentals
- Why connecting over non-standard ports boosts security
- Simple steps for setup using Google tools
- Extra methods for other SSH clients
- Best practices for hardening cloud VMs further
My goal is to fully demystify this process so you can flexibly access VMs however needed, while following cybersecurity industry recommendations. Because obscuring your attack surface shouldn‘t be obscure at all!
So whether you‘re an absolute beginner or seasoned cloud pro – let‘s unlock the power of custom ports on GCP together.
An SSH Refresher – Setting the Stage
Before jumping to non-standard connections, a quick primer on SSH itself can set the stage…
SSH, or Secure Shell Protocol, facilitates remote login and command execution in a secure way. Using encryption, it allows securely interfacing with systems over unsecured networks.
The most common implementation is OpenSSH. This consists of a daemon (sshd) running on servers, and client apps (ssh) for remote access.
Authentication works through usernames/passwords and/or cryptographic key pairs. So only verified identities can administer servers, providing access control and auditability.
Now what about the networking piece?
To enable finding specific services for connection requests, systems assign numbered ports for different applications. Some standard allocations include:
- HTTP web traffic – Port 80
- HTTPS encrypted web traffic – Port 443
- SMTP email relaying – Port 25
And for SSH itself…the default port is 22.
So in summary:
- SSH = Secure remote access protocol
- Port 22 = Default network channel that SSH communication happens over
This handles most use cases well. But as we‘ll explore next, the very predictability that enables connectivity also introduces security issues…
Why Connect to Custom Ports for Enhanced Security
Opening any internet-facing entry point inevitably increases a system‘s exposure to attacks. And with remote command execution and data access abilities, SSH capabilities warrant particular caution.
Malicious actors routinely scan wide swaths of IP address ranges looking for responders on common ports like SSH. They then launch brute force password guessing and exploit scripts to try gaining access.
In fact, studies show over 90% of successful cyberattacks specifically target SSH weaknesses as an initial access vector.
So while blocking SSH entirely may not be practical for administration needs, can we still lower risks?
This is where non-standard SSH ports shine!
Obscuring from the default port 22 to another high numbered port achieves:
1. Security through obscurity – Attackers blindly seeking out the usual ports will miss yours. This discourages opportunistic hacking.
2. Raises cost to target you – Forcing custom enumeration for discovery and then tailored attacks requires far more effort.
3. Obfuscation buys time – Even an extra few steps means chances of noticing and responding to contain threats.
While not a cure-all, moving off predictable ports meaningfully improves security posture. It also costs virtually nothing to implement for your Google Cloud VMs!
Let‘s look at how to put this into practice…
Step-by-Step Guide: Accessing GCP VMs Over Custom SSH Ports
Google makes alternating SSH ports a breeze across their tooling. I‘ll share multiple methods to fit different needs:
- gcloud CLI – Powerful commands for scripting or automation
- Browser-based SSH – Clickable simplicity, no client required
- External client – Utilize existing SSH apps you already know
We‘ll also cover best practices for even more locked down security. Let‘s get started!
Prerequisites
First, you‘ll want to:
- Have an existing GCP VM Instance created in Compute Engine
- Configure its network tags and firewall rules to allow SSH over chosen custom port
- Enable the VM to accept SSH logins on that new port
These steps happen directly on the VM itself. But once set up, you won‘t need to touch it again.
Now let‘s securely connect from our local machine…
gcloud CLI Access
Google‘s gcloud command line tooling allows managing cloud resources right from terminal or shell. This includes SSH directly into running VM instances.
To link gcloud to non-standard ports:
- In the GCP Console, navigate to Compute Engine > VM Instances
- Click the dropdown arrow beside "SSH"
- Choose "view gcloud command"
- A sample string will populate automatically with basic syntax
- Append the
--ssh-flag="-p"parameter and your desired port to the end
For example, with VM "my-server" using SSH port 4444:
gcloud compute --project "cool-project-1234" ssh --zone "us-west1-a" "my-server" --ssh-flag="-p 4444"Executing this will securely tunnel over port 4444 rather than default 22.
The gcloud shortcut makes quick connections in scripts or terminals a breeze while avoiding exposing additional surface.
Browser-Based SSH Web Preview
For secure access without locally installed tools, Google provides one-click browser connections.
From Compute Engine > VM instances:
- Choose "SSH" drop down
- Select "Open in browser window"
- Authorize the popup dialog
- Receive interactive shell prompt right in your tab!
To specify custom ports:
- Choose "Open in browser window on a custom port"
- Supply your alternate SSH port number
- Click Open
A separate tab will fire up with login over that port instead of default.
It handles SSH key auth, proxies tunnel securely through Google‘s network, and works on any device with a browser. Convenient for managing servers from anywhere!
Between gcloud automation or browser jumps, you have flexible options tailored to admins of any skill level.
But for those who prefer external tools…let‘s explore that next.
Third Party SSH Clients
If you have an existing SSH client like PuTTY or OpenSSH, we can bridge that over as well:
- Find the external IP address for your GCP VM Instance
- Specify your new custom SSH port in the client configuration
- Connect using SSH credentials as usual
For example, with OpenSSH:
ssh -i my-private-key [email protected] -p 4444Routes through the external IP first to reach the Compute Engine internal network, before authorizing and tunneling the SSH session over our non-standard port.
This keeps your workflow in already familiar environments.
Security Best Practices
Obscuring SSH away from its common port slashes attack surface. But we can harden things further with additional measures:
- Require SSH key pairs over passwords
- Restrict source IP ranges on firewall ingress rules
- Enable Cloud Armor for adaptive protection
- Rotate credentials routinely per security policy
- Analyze Cloud Audit Logs for suspicious patterns
- Keep OS and software updated with latest patches
Combine obscurity with proactive hardening for defense in depth.
Key Takeaways
Migrating SSH in Google Cloud VMs to non-standard ports may seem intimidating. But with built-in guidance from Google‘s tooling, it ends up quite straightforward:
- Drop-in flags for
gcloudCLI access - Effortless browser-based connections
- Bridging external SSH clients through public IP
Blending these techniques with strong authentication, tightly scoped firewall rules, audit log analysis, and other security best practices significantly raises the effort for would-be attackers.
So don‘t shy away from rolling out custom ports because of perceived complexity. Instead, wield them confidently knowing Google Cloud has your back!
What ports will you choose for your next VM project? I‘m always happy to help explain any piece in more detail. Until next time my friend – may your cloud journeys lead to more light than shadows.
