How to Secure the Mainframe: The Core of Banks and Governments

Remember that scene in Mission: Impossible where Ethan Hunt drops into a high-security vault and yet everything still seems like it could go wrong? That works because it touches a very real fear: even the most secure systems can be vulnerable. In the digital world, the equivalent of that high-security vault is the mainframe.

At TecnetOne, we often explain it this way: if your organization were a body, the mainframe would be the heart. It's not visible from the outside, but it pumps every transaction, every query, every critical piece of data that keeps operations alive. That’s why securing it isn’t optional or “something to do later”—it’s a critical business requirement.

What Is a Mainframe and Why Does It Matter So Much?

A mainframe is a transactional system designed to handle massive volumes of real-time operations with extreme reliability. It powers:

1. Banks processing uninterrupted payments
   
   
2. Airlines managing reservations and boarding in seconds
   
   
3. Governments storing and retrieving tax, health, or identity records

We’re not just talking about performance—we’re talking about continuity. Mainframes are designed to avoid losing a single transaction, even under heavy load, thanks to architectures with queues, redundancy, and fault tolerance.

That’s why if someone breaches a mainframe, the consequences are immediate. An attacker could:

1. Initiate fraudulent transactions
   
   
2. Access sensitive citizen or customer data
   
   
3. Manipulate critical records
   
   
4. Interrupt essential services

Mainframes remain the core operational engine behind a significant portion of the global financial and governmental infrastructure—making them a highly attractive target.

The Heart That Powers the Largest Enterprises

Nobody knows the exact number of financial transactions processed every second globally, but there are too many zeros for failure to be an option.

So how do large organizations handle that scale without collapsing? Through platforms like:

1. IBM z/OS
   
   
2. AS/400 (IBM i)
   
   
3. HP NonStop
   
   
4. Fujitsu GS21

Mainframes are deeply integrated into everything. In a bank, for instance, every action you perform—from web to mobile, call center to ATM—ultimately hits the mainframe via a typical flow:

1. The user interface sends a request
   
   
2. The request flows through channel APIs
   
   
3. Middleware translates and routes it
   
   
4. The mainframe processes the transaction and returns the result

It’s efficient—but it also means that attacking any part of the flow (like APIs or middleware) can lead directly to the core.

Read more: The Quantum Era and Airlines

Why Securing Just the APIs or Middleware Isn’t Enough

Most companies invest more in what’s visible: web and mobile apps, APIs, WAFs, gateways. That’s where audits and attacks are more obvious.

The problem? Many fall for this false assumption:

“If we protect the front-end, nobody will reach the mainframe.”

That’s simply not true.

Modern attacks unfold in stages:

1. Compromise a user via phishing or leaked credentials
   
   
2. Exploit excessive permissions
   
   
3. Move laterally within the network
   
   
4. Find forgotten or weak integrations
   
   
5. Reach critical systems
   
   
6. Perform malicious but technically valid operations

If the mainframe trusts that all validation happens upstream, it becomes the weakest link. That’s why core-level controls are non-negotiable. You need defense in depth—no exceptions.

The Pillars of Mainframe Security

There’s no magic trick here—just discipline. A robust mainframe security strategy is built on consistent technical and operational decisions.

1. Design With Core-Level Security in Mind

Don’t treat the mainframe as untouchable legacy. Instead, ask: What security controls must live inside the mainframe itself, so that even if other layers fail, the core remains safe?

2. Minimize Its Exposure

Ideally, the mainframe should only talk to a limited number of systems—usually just the middleware translating API requests.

Fewer pathways = fewer attack vectors.

3. Enforce True Least Privilege

In critical environments, excessive permissions are not just bad—they're dangerous. Review:

1. Who has access
2. What they can do
3. When and from where
4. With what audit levels

If someone doesn’t need a permission—they shouldn’t have it.

4. Implement Privileged Access Management (PAM)

PAM solutions help monitor and control high-risk accounts: admins, operators, service accounts, etc.

If you can’t control it, you can’t protect it.

5. Manage Changes and Patch Often

Mainframes evolve too. Implement structured change management:

1. Apply security and functional patches
2. Validate configuration changes
3. Test thoroughly before going live
   
   

6. Log, Audit, and Limit Sessions

When something happens, you need evidence. And if someone tries something malicious, you need alerts. So:

1. Enable detailed activity logging
2. Define strict logging policies
3. Use short-lived sessions and one-time credentials
   
   

7. Test in Preproduction

The mainframe is too critical to test changes in production. Always validate in a preproduction environment to avoid unexpected breaches or failures.

You might also be interested in: Is the Mexican Government Being Hacked by Its Own Employees?

Cybersecurity Services That Actually Improve Defense

Beyond controls and processes, three services help you move from “compliant” to resilient.

Threat Hunting

Proactive analysis that assumes the attacker is already inside. It works with hypotheses: “If an attacker were here, what traces would they leave?”

It’s the only way to detect stealthy threats before they become incidents.

Red Teaming

Simulates real-world attack scenarios to test your defenses, not your policies. If your organization follows standards like DORA, TIBER-EU, or NIS2, this isn’t optional—it’s expected.

Advanced Pentesting

Helps uncover vulnerabilities in or around the mainframe and its integrations. It’s a technical snapshot that complements Red Team insights.

Final Thoughts: Secure the Core, Secure the Business

Banks, airlines, governments, insurers, and large retailers rely on transactional systems to function. That’s why the mainframe is a high-value target.

The takeaway is simple: securing the front-end isn’t enough. Yes, APIs and middleware matter—but the real risk is at the core.

At TecnetOne, we put it this way: If an attacker gets a malicious operation to the mainframe, you could face millions in losses and hard-to-repair reputational damage.

Mainframe security is not just a technical task—it’s a strategic decision to keep your organization running.