5 Critical Security Mistakes Developers Still Make in 2026

No software developer sets out to write insecure code. But it happens, even in 2026. In fact, software developers are often in a rush to deliver results within deadlines and budgets, and they knowingly or unknowingly cut corners. This can lead to a myriad of issues down the road, with security holes at the top of the list.

And in the world of software, poor security can be really expensive. According to IBM, data breaches in 2025 cost companies a staggering $4.4 million yearly. This number shows that even the "smallest" oversight can have serious consequences. What’s frustrating is that many of these breaches come from basic mistakes developers keep making year after year. 

In this guide, we’ll discuss five of these security mistakes. We'll also talk about how to know you've made them and how to fix them. Read on.

Mixing Up Authentication and Authorisation

Authentication and authorisation get thrown around like they mean the same thing. They don’t. Authentication checks who the user is, while authorisation determines where they can go and what they can do. 

That someone can log in successfully doesn’t mean they should have access everywhere in the system.

The good news? Spotting this mistake is fairly straightforward. 

Start by reviewing your API endpoints and backend services. Check where “is authenticated” is being used as a substitute for proper permission checks. Also, make sure authorisation is enforced server-side and not just in the frontend, since frontend checks can be bypassed easily.

Next, look for missing roles or permissions. Known as Broken Access Control, this issue is No. 1 in the OWASP Top 10 risk list, and causes over 1.8 million breaches.

How to Prevent or Fix This Mistake

Fixing it is also pretty straightforward. Use role-based access control (RBAC) or attribute-based access control (ABAC) to clearly define who has access to what. Also, consider applying the principle of least privilege. The idea is to give each user only the access they need to do their jobs. Nothing more.

Overlooking Data Security and Encryption

Software devs sometimes focus so much on the "front door" that they forget about what's happening in the "back room." Unfortunately, leaving data unencrypted, either at rest or in transit, is like leaving your house keys in the lock. Things get stolen.

To know if you made this mistake, check your database. 

Can you read passwords, emails, or personal info in plain text? 

If you can, then you have a problem. You should also check how your app talks to other services. Is everything moving over HTTPS? Plain old HTTP is a problem waiting to happen. 

How to Prevent or Fix This Mistake

To fix or prevent data encryption mistakes is simple: Encrypt everything. Use AES-256 for data at rest and enforce TLS for data in motion. Anything less and you could be seeing a very expensive breach in the near future. 

A typical example is the PayPal working capital data exposure of 2025, which exposed the Social Security numbers of thousands of customers for six months. 

While encryption wasn’t the root issue, the incident highlights a broader failure in data security.

Overlooking Monetisation Risks

This one's a trap a lot of developers fall into when they're building their first SaaS product or adding a billing layer to an existing app. The logic is that: "I'll just collect card details, send them somewhere, and figure out compliance later." 

That "later" can cost you as much as $100 a month in PCI non-compliance fees. That doesn't include any breach costs.

So, ask yourself: does your app ever touch raw card numbers? Does cardholder data pass through your servers at any point? If yes, then you may have a problem you don't even know about.

How to Prevent or Fix This Mistake

So, how can you fix this? The simplest answer is to not handle raw payment data yourself. Use a payment provider to handle the technical aspect. 

According to PayPro Global, you need the right platform to manage payments, taxes, compliance, and so on. Get that right, and you're free to focus on building a solid product.

Maintaining Active Backdoor Accounts

Many developers do this. They add a hardcoded admin account during testing, maybe "just for QA," and then forget about it. The product ships. Two years later, an attacker finds it and uses it.

This would have been funny if it hadn't actually happened in real life.

Just recently, Dell's RecoverPoint for Virtual Machines product was found to contain a hardcoded credential flaw that Chinese state-sponsored hackers had been exploiting since mid-2024.

It's like Dell engineers just handed an attacker a skeleton key to the hackers and said, "get on with it."

How to Prevent or Fix This Mistake

To check whether you made this mistake, audit your user database. Check for accounts with generic names like "admin," "test," or "dev." Also, check your environment variables and config files for hardcoded credentials. 

If you find a "backdoor" that doesn't require MFA, kill it immediately.

Ignoring Layer 8

You can build the most secure and user-friendly software in the world. But that won’t matter if people misuse it. This is what Layer 8 means. This is the human factor in software use, and honestly, it’s often the weakest link.

The data is clear on this: 95% of cyber incidents involve some form of human element. Unfortunately, no amount of encryption can prevent someone from falling for a phishing message and pasting credentials into a Slack message.

But you can know how weak your Layer 8 is. How? By checking how people actually interact with your software system. Check for weak password policies, and if possible, simulate phishing or social engineering scenarios. If users can fall for your ploy, it shows that they can fall for phishing attacks.

How to Prevent or Fix This Mistake

Fixing this problem doesn't involve a lot of technicalities. It simply requires security awareness training, including how to use strong authentication. It needs to be practical, scenario-based, and repeated.

You may not completely eliminate human error. But you can train users not to ignore it.

Build Secure, Ship With Confidence

Most, if not all, the security mistakes covered in this guide come down to habits rather than knowledge gaps. Virtually every software developer knows what to do. The tricky part is making good security practice automatic. 

But you can, by continuous learning.

Of course, you don’t need to do everything at once. But you need to start. Why? Because attackers aren’t waiting. And they’re not always using advanced tricks. Sometimes, they’re just waiting for you to miss the obvious.