What Is OWASP A06:2025 Insecure Design?
OWASP A06:2025 – Insecure Design refers to security weaknesses that originate from flawed architectural and workflow decisions rather than from coding mistakes or configuration errors. Insecure design occurs when applications and APIs are built without essential security controls, rely on assumptions of trusted user or client behaviour, and fail to account for abuse cases and attacker-driven workflows.
These design gaps often include the absence of explicit authorization checks, missing rate limits, and inadequate input validation rules. Insecure design vulnerabilities cannot be easily patched after deployment. They are frequently embedded deep within application logic, APIs, and business workflows, making remediation complex and disruptive.
The OWASP Top 10 2025 dataset highlights insecure design as a growing risk category because modern applications increasingly expose complex business logic through APIs, automation, and distributed services, significantly amplifying the impact of design-level security gaps. 
Why Insecure Design Is a Top Risk in OWASP Top 10 2025
Insecure design remains a top risk because application architectures have evolved faster than security design practices.
Key trends increasing exposure include:
API-first and microservices architectures
Applications now expose hundreds of APIs that directly map to business functions. When these APIs are designed without explicit authorization, abuse controls, or rate limiting, attackers can exploit logic vulnerabilities at scale.
Imagine a banking app that lets you view your profile via a specific URL. If the developers designed that API to fetch data based solely on a user ID in the link without double-checking if you are actually the owner of that ID, they have built a fundamental flaw into the blueprint. An attacker does not need to hack the system in the traditional sense. They just have to change a number in the URL to scroll through thousands of private records.
Speed-driven development cycles
In the rush to hit a launch date, security is frequently treated like the paint on a house rather than the foundation.
Take a password reset feature for example. A team might implement a quick four digit PIN system to save time and skip the deep threat modeling that would have flagged how easy that is to guess. Without a design-level lockout or a more complex token, they have essentially handed a master key to anyone with a basic brute-force script.
Assumption-based trust models
This connects directly to systems that simply assume everyone will play by the rules. You see this often in e-commerce workflows. A designer might trust that the price shown on a checkout page is the price the customer will pay. However, if the server does not re-verify that price against the database at the final moment of purchase, a savvy user can intercept the request and change a five hundred dollar item to five dollars. The system trusts the data coming from the browser and that trust is exactly what gets exploited.
Overreliance on perimeter security
Finally, there is a need to balance perimeter defenses with internal design controls. Tools like Web Application Firewalls are essential for blocking common exploits and malicious traffic patterns, acting as a critical first line of defense. However, they are most effective when the application’s internal logic is also secure. For instance, if a referral program is designed with a flaw that allows a user to refer themselves multiple times, the traffic may appear entirely legitimate to a firewall. Because there is no malicious code or “attack” signature to catch, the user is simply following a broken workflow. Robust security requires both a strong perimeter and a design that handles business logic safely from within.
Common Insecure Design Vulnerabilities in Production Applications
Insecure design weaknesses are repeatedly observed across real-world applications and APIs.
Missing authorization at the object and workflow level
This is essentially a failure to check the “ID” of the person requesting a resource, much like the banking example we discussed earlier. While that scenario focused on accessing an account, the same flaw can be even more sensitive in other contexts, like healthcare. Imagine a medical portal where, after logging in, you can see your lab results at a URL ending in /results/9876. If the system is designed to show whatever result matches the number in the URL without confirming that result 9876 actually belongs to you, the door is wide open. An attacker can simply increment the numbers to view the private health records of every other patient. This is not a coding bug so much as a failure to design an ownership check into the very flow of the data request.
Abuse-prone business logic
Designs in this category fail because they do not account for how a feature can be used too well. Consider a retail app that offers a ten dollar discount code for new sign-ups. If the design does not include a way to tie that code to a verified identity or a unique device, a single user can automate the creation of a thousand accounts to hoard ten thousand dollars in credit. The application is doing exactly what it was told to do by issuing a coupon to a new user, but the design lacked the necessary friction to prevent the business model from being turned against itself.
Lack of rate limiting by design
Many applications are built with the optimistic assumption that users will behave at a human pace. When a design fails to define what normal usage looks like, it becomes a playground for automation. For example, a quote generation tool for insurance might be designed to provide a response in seconds. Without a per-user or per-IP limit designed into the service, a competitor could script a bot to request millions of quotes an hour. This does not just scrape your pricing data. It can overwhelm your backend services and effectively turn a useful feature into a self-inflicted denial of service attack.
Trusting client-side controls
This is the digital equivalent of a store leaving the key to the display case in the lock and just asking customers not to turn it. A developer might design a web form where admin features are simply hidden using a bit of code. The assumption is that if the user cannot see the button, they cannot click it. However, since the underlying server-side logic does not actually check for admin credentials when the request arrives, a user who knows how to inspect the page code or send a direct request can bypass the UI entirely and execute privileged commands.
APIs designed without threat modeling
When APIs are built in a vacuum, they often end up exposing the internal guts of the system. A mobile app might call an internal API that returns a massive data object containing a user profile, including a home address and internal database ID, even though the app only needs to display a first name. The designers assumed that because the mobile UI only shows the name, the rest of the data is safe. But because the API was never threat-modeled for external exposure, that sensitive data is sitting right there in the network traffic for anyone with a proxy tool to read.
Insecure Design vs. Security Misconfiguration
A common misconception is to treat insecure design as a configuration vulnerability.
| Aspect | Insecure Design | Security Misconfiguration |
|---|---|---|
| Root cause | Architectural decision | Deployment or setup error |
| When it occurs | Design and planning phase | Build or runtime phase |
| Ease of remediation | High effort | Medium to low |
| Example | No authorization checks in workflows | Public admin endpoint enabled |
Insecure design defines what the application is allowed to do, not how securely it is deployed.
Business Impact of Insecure Design
Insecure design directly translates into business risk because it enables attackers to abuse legitimate functionality.
High-cost architectural debt
Fixing a design flaw is fundamentally different from patching a line of code. When a vulnerability is baked into the architecture, remediation often requires redesigning entire APIs, workflows, or authorization models. This is a massive drain on engineering resources and can delay product roadmaps by months. Unlike a quick software update, these changes require deep structural work and extensive regression testing, making “fixing it later” one of the most expensive decisions a business can make.
Undetectable “silent” breaches
Because these attacks involve abusing legitimate functionality, they often leave no traditional “smoking gun.” A Web Application Firewall or an intrusion detection system might see perfectly valid traffic because the attacker is simply following the path the designers laid out. This creates a high risk of long-term, undetected data exposure. By the time a company realizes that their records have been enumerated or their coupons have been drained, the financial and reputational damage is often already widespread.
Compromised business integrity
Insecure design does more than just leak data; it can break the very logic of your business model. When pricing logic can be manipulated or referral programs can be automated for fraud, it creates a direct hit to the bottom line. This type of abuse erodes trust with partners and customers who expect a level playing field. If the fundamental rules of your application can be rewritten by a savvy user, the integrity of the entire service is called into question.
Regulatory and compliance friction
From a compliance perspective, design-level failures are particularly damaging because they often point to a lack of “Privacy by Design” or “Security by Design.” Regulations like GDPR or industry standards like PCI-DSS do not just care that you have a firewall. They care that you have enforced strict access controls between users and tenants. A design that allows one user to see another person’s data is a direct violation that can lead to heavy fines, mandatory audits, and a long road to regaining regulatory standing.
How Attackers Exploit Insecure Design
Attackers exploit insecure design by abusing intended application behavior, not by breaking or bypassing security controls. The application responds exactly as designed, just in ways the designers did not anticipate.
They typically:
Enumerate APIs and workflows
Attackers systematically map APIs, endpoints, and application flows using automation. By observing patterns in requests, responses, and object identifiers, they identify how data and actions are structured and where controls are weak or inconsistent.
Identify missing authorization or validation
Once workflows are mapped, attackers look for gaps in authorization, ownership checks, and input validation. This includes accessing objects they should not see, performing actions out of sequence, or invoking privileged functions without proper checks.
Abuse business logic at scale
After finding a design weakness, attackers automate it. Instead of exploiting a vulnerability once, they repeat it thousands of times, extracting data, manipulating transactions, or exhausting resources and turning a small logic gap into a large-scale impact.
Chain design vulnerabilities with other vulnerabilities
Insecure design is often combined with other weaknesses such as weak authentication, excessive permissions, or exposed APIs. Chaining these vulnerabilities allows attackers to escalate access, move laterally, or achieve deeper compromise.
Because these actions closely resemble legitimate usage, insecure design attacks are difficult to detect, hard to distinguish from normal traffic, and rarely blocked by traditional security controls.
How to Reduce Risk from Insecure Design in Applications
Addressing insecure design requires intentional security decisions during architecture and design, combined with runtime enforcement.
Design security controls explicitly
Security controls must be treated as first-class design requirements, not implementation details. Every workflow should clearly define authentication requirements, authorization checks, rate limits, and failure handling. If these controls are not explicitly designed, they are often inconsistently implemented or missed entirely, creating opportunities for abuse.
Perform threat modeling early
Threat modeling should focus on how attackers misuse functionality, not just how legitimate users interact with the system. Teams should evaluate abuse cases such as automation, parameter manipulation, workflow skipping, and privilege escalation. Identifying these risks early prevents insecure patterns from becoming embedded in core architecture.
Apply consistent security logic across APIs
Insecure design often emerges from inconsistent enforcement across APIs and services. Object-level authorization, input validation, and rate limiting must be applied uniformly across all endpoints, including internal, partner, and legacy APIs. A single weak endpoint can undermine the security of the entire application.
Use defense in depth
Design-time controls significantly reduce risk, but they are not sufficient on their own. Runtime protections such as behavior monitoring, anomaly detection, and abuse prevention are essential to protect against unknown attack techniques, design oversights, and legacy components that cannot be easily redesigned.
Validate design through business logic testing
Traditional vulnerability scans rarely detect insecure design because no technical exploit is required. Business logic–focused penetration testing helps uncover how legitimate functionality can be abused, including workflow manipulation, authorization bypasses, and automation at scale.
Solutions like AppTrana WAAP combine DAST scanning with expert-led penetration testing for business logic vulnerability identification. This approach allows organizations to identify insecure design weaknesses and apply compensating runtime protections, reducing risk while long-term architectural fixes are planned.
Developer Checklist: Preventing Insecure Design (OWASP A06:2025)
This checklist converts mitigation principles into practical actions.
1. Authentication and Authorization
- Enforce authentication on all sensitive workflows
- Validate authorization at the object and function level
- Never trust client-supplied identifiers or roles
2. Business Logic Protection
- Define limits for sensitive actions (resets, retries, redemptions)
- Detect and prevent automated abuse patterns
- Validate workflow sequencing server-side
3. API Design Controls
- Enforce schema validation on all APIs
- Apply object-level authorization consistently
- Avoid exposing internal data models directly
4. Rate Limiting and Abuse Controls
- Apply per-user, per-token, and per-function limits
- Design APIs assuming automation, not human behavior
5. Trust Boundary Enforcement
- Treat all external input as untrusted
- Avoid relying on UI or client-side enforcement
6. Error Handling and Edge Cases
- Handle failure states securely
- Avoid logic bypass through unexpected input combinations
7. Threat Modeling and Reviews
- Include security design reviews in SDLC
- Re-evaluate design when adding APIs or workflows
8. Legacy Application Controls
- Identify insecure design patterns in legacy systems
- Apply compensating runtime controls where redesign is delayed
