The Security Vulnerabilities Hiding in Your Mendix Application

This article is not going to address the obvious issues like missing entity access rules. I'm going to talk about the subtle vulnerabilities that pass code reviews, make it through testing, and sit quietly in production until someone discovers them – hopefully, that someone is you and not a malicious actor.

Your Mendix application probably has security vulnerabilities you don't even know about.

I have compiled the most common vulnerabilities that developers consistently miss. Some of these might make you immediately want to check your own applications. That's exactly the point.

Mendix and Security

Using a low-code platform doesn't automatically make your application secure. While Mendix provides excellent security features, they're only effective when properly implemented.

The platform can't protect you from:

• Architectural decisions that expose sensitive data

• Business logic that bypasses security rules

• Misconfigurations that create attack vectors

• Developers who don't understand security implications

Think of Mendix security features like locks on doors at your house or office – they're only effective if you remember to use them correctly.

The Most Common Vulnerabilities in Mendix Applications

1. Anonymous User Role Misconfigurations

This is perhaps the most prevalent and dangerous vulnerability I encounter. Developers often grant anonymous users far more access than intended.

Common mistakes:

• Microflows and Nanoflows marked as "accessible by anonymous users" that shouldn't be

• REST endpoints without proper authentication requirements

• Entities marked with read and write access for all user roles

2. Client-Side Logic Exploitation

Mendix makes it easy to execute JavaScript inside nanoflows, but many of us don't realize that this logic is visible to anyone who opens their browser's developer tools.

Critical mistakes: Calculating business logic, Storing API keys or credentials in JavaScript actions

3. Weak Input Validation

Input validation in many Mendix applications often stops at the UI level, but that's like locking your front door while leaving the back door wide open.

Critical mistakes:

• Validation only in client-side widgets

• XPath expressions constructed from user input (hello, SQL injection!)

• File uploads without proper type and size validation

• Text inputs that accept HTML or scripts

Best practice: Always validate and sanitize input server-side, regardless of client-side validation.

4. Data Exposure Through Associations

Mendix's automatic data retrieval through associations can expose more information than intended.

Common mistakes: Entity access rules that don't consider association paths

Best Practice: Never assume association security. Explicitly define what users can see through every path.

5. Session Management Weakness

Session security in Mendix applications often receives minimal attention during development, specially in cases when SSO logins are used.

Common mistakes: Logout buttons that don't properly clear sessions

Best Practice: On signing out users that authenticated with SSO, end the SSO session as well along with Mendix session.

6. Default Configurations in Production

This category makes security professionals weep. Production applications running with development configurations.

Common mistakes:

• Admin passwords still set to "1" or "Admin123"

• Demo/Test users active with known passwords

• Exposed Constants containing hardcoded credentials

• After Startup microflow with test data creation

7. Insecure File Handling

File handling requires careful consideration of security implications.

Common mistakes:

• No virus scanning on uploads

• Storing sensitive files in publicly accessible locations

• No encryption for files at rest

• Missing file type restrictions

8. Incomplete Access Control

Beyond entity access, there are numerous access control gaps in typical Mendix applications.

Common mistakes:

• Page access rules not aligned with entity access

• Microflow access more permissive than necessary

• REST endpoints without proper checks

9. Audit Trail Blind Spots

Security isn't just about prevention – it's about detection and response.

Common mistakes:

• No logging of sensitive data access

• Missing audit trails for configuration changes

• No monitoring of failed authentication attempts

• Lack of alerts for suspicious patterns

• Logs that don't capture enough context for investigation

The Path to Secure Mendix Applications

Identifying vulnerabilities is only the first step. Here's how to systematically improve your application security:

1. Security-First Architecture Design with security as a primary concern, not an afterthought. Every architectural decision should consider security implications.

2. Regular Security Audits Schedule quarterly security reviews. Fresh eyes often catch what familiar ones miss.

3. Developer Security Training Invest in security training specific to Mendix. Understanding the platform's security model is crucial.

4. Security Champions Designate security champions within your development team who stay current on security best practices.

5. Penetration Testing Invest in penetration testing that is performed by an external agency after every major release of your application.

Conclusion

Security vulnerabilities in Mendix applications aren't inevitable but they're preventable.

Prevention requires acknowledging that low-code doesn't mean low-risk. It requires understanding the platform's security model deeply and implementing it correctly.

The vulnerabilities I've outlined aren't exhaustive. They're simply the most common ones I encounter. Your application might have unique vulnerabilities based on your specific implementation.

That's why I want to hear from you: What security vulnerabilities have you discovered in Mendix applications? How did you find them, and more importantly, how did you fix them? Share your experiences in the comments. Your insights could help secure someone else's application.

In security, we're all on the same team. The more we share about vulnerabilities and fixes, the stronger our collective defense becomes.

Stay tuned for next week's article where we'll dive into performance optimization – because a secure application that users can't efficiently use is still a failed application.

And if you're serious about testing your Mendix security knowledge, mark your calendar for our Capture the Flag event in Montreal this October. It's the perfect opportunity to safely explore security vulnerabilities in a controlled environment.