Revolutionizing Firewall Security with Least Privilege and Zero Trust

Here I am, sitting at my desk — third cup of coffee kicking in — thinking about its implications on least privilege and Zero Trust, specifically, and how it really, really changes the game for firewall security. For groups like mine, which have been around since the 90s (I started out as a network admin in ‘93), this has been a continually evolving space — from managing voice and data muxes over PSTN to surviving the Slammer worm. Now that I run P J Networks, getting businesses — now including three large banks — to kick their Zero Trust architecture into high gear is what keeps me buzzin’. The other thing is: I just came back from DefCon and I’m still all XTREME-d out from the hardware hacking village. It’s interesting because it demonstrates that firewall security is still a key foundational element of strong Zero Trust strategies.

Least Privilege Explained

Here’s the thing about least privilege: it’s not a buzzy term the security people like to say to sound cool. It signifies that users, devices, applications — everything — has access only to what it actually requires, and nothing else. Period.

When I first got into networking, we just blindly trusted the network because, it pretty much had to work that way. You connected, you got online. But those times are long past — thank goodness. The Slammer worm was the wake up call: no firewall rules? Boom, full systems breached in minutes.

Zero Trust flips that old way of thinking on its head. A wise man once said, don’t trust anyone or anything inside or outside your network without it being properly verified. And what about the firewalls to enforce least privilege? It’s the frontline.

The way I imagine it is how you drive a car. It’s not like just because you’re at the driver’s seat it will give you access to the engine’s guts or whatever it uses to steer—it only gives you the controls you need to drive safely to get wherever the hell you’re going. Firewalls do this in the digital realm.

Firewall-Based Access Rules

Firewalls are not just highway traffic cops screening out bad things. When implemented well, they are gatekeepers who impose narrow access control policies and least privilege. And this is where too many companies fall down. They set generic allow rules, like “allow all the traffic from this subnet,’’ and essentially fling the door open.

At P J Networks, we’ve worked with banks to surgically remodel their zero trust upgrades of their firewall rules:

• Define source and destination IPs accurately. No vague IP ranges.
• Define the specific ports and protocols. If you don’t require that SMB or RDP be open, close it off.
• App-level filtering. Some firewalls can even allow you block applications, not just ports.
• Organize the flow of traffic by zones and interfaces with firewalls.

And it’s not “set and forget.” The firewalls should learn and change as your deployment does. That’s why lots of people advocate for automation—but I’d say, be careful there, especially with “AI-powered” solutions. I’ve watched flashy demos that overpromise and underdeliver. The human eye and continuous tuning do still count.

Micro-Segmentation

Micro-segmentation is one of the things that has changed the game for Zero Trust adoption in a major way. It’s the equivalent of taking your internal network and slicing it up into smaller, more tightly controlled segments, each with that special-purpose firewall, so if something goes wrong, it’s contained.

I have seen a bank that I was supporting recently where they separated out the entire payment processing workflow from their general office operations. The firewall rules were so strict that even if an attacker got into a workstation, it was nearly impossible to move laterally.

It’s sort of like cooking with those compartmentalized pots: You don’t want your spicy curry spilling into the dessert sauce. Each has its own space, controlled heat and careful oversight.

A few fast micro-segmentation pointers to get you going:

• Prioritize in order of importance to the mission.
• Layering controls with network ACLs, host-based firewalls and endpoint security.
• Leverage software-defined networking (SDN) if your infrastructure enables it for dynamic security segmentation.
• You should always map out communication flows before blocking anything.

Identity Verification

Firewalls are not sufficient. Zero Trust, when I talk about Zero Trust, identity is the soul of the whole thing.

Firewall rules were, in the early times, mostly network-based/IP-based. But in today’s Zero Trust policies, identity is king. Firewalls connected to identity providers puts you in the position to easily build access rules based not only on where traffic is coming from but also who makes the request — users and machines alike.

Consider multi-factor authentication (MFA) with firewall polices…and that one shouldn’t be up for discussion according to me. That extra layer can spare you so many headaches. And don’t even get me started with the password policies — quit mandating 90-day resets; it’s 2024, people. I’ve argued for better alternatives like passphrases and behavioral analytics, which frankly, work better than random resets.

But there is a catch — identity has to be constantly reconfirmed. Not just at login. Firewalls must allow for dynamic reauthentication or just-in-time access changes. That way, not even an inmate who has compromised an account gets persistent access.

Ongoing Audits

One mistake committing in the past (and, to be honest, it was this very mistake that kept me up at night)—treating a firewall configuration as a project with a finish line. Nope. Firewall security is a long-distance run, not a sprint.

And policies must be reviewed and updated on a regular basis. Threat landscapes shift. Business needs evolve. And so, too, must your firewall rules.

Below is what we do for our clients at P J Networks:

• Quarterly review of your firewall policy
• Ongoing logs analisys and anomaly detection
• Automatic notes on any unauthorized configuration changes
• Network penetration testing and attacker simulation to verify access controls

And honestly, I’ll be a little brusque—if you’re not regularly reviewing those firewall rules, you’re just hoping security will work out. Hope isn’t a strategy.

Quick Take

• Zero Trust is only successful when least privilege is in place.
• Firewalls should be able to enforce granular access rules, not blanket permits.
• Micro-segmentation slices and dices your network into bite-sized, secure chunks.
• Identity-based verification that is embedded into firewall policies secures access.
• Audits and reviews keep your Zero Trust position sharp and up to date.

And finally — Zero Trust is not magic, and firewalls alone don’t fix everything. However, when you couple tight firewall-based access controls with identity validation, micro-segmentation and continuous vigilance, you’re building a defense that’s not only strong — it’s intelligent.

And, trust me, after decades in the middle of this thing — from the heady days of PSTN muxes to today’s cloud frenzy — that’s not going to be a shortcut. Embrace the firewall, don’t treat it as an afterthought. Because that’s how least privilege gets going — at the edge.