The OWASP Top 10 is the industry's reference list of the most critical web application security risks. Knowing the names is not the point. Knowing exactly how to prevent each one in the code you actually write is. This guide walks the categories and the concrete defence for each in a modern JavaScript stack, and pairs with our broader API security checklist.
Broken access control
The most common serious flaw: users acting outside their intended permissions. Enforce authorisation on the server for every request, never trust the client to hide a button, and check ownership on every record a user tries to read or modify. Deny by default and grant explicitly.
Cryptographic failures
Sensitive data exposed through weak or missing encryption. Use TLS everywhere, hash passwords with a strong adaptive algorithm, encrypt sensitive data at rest, and never invent your own cryptography. Most failures here are about using the wrong tool, not a broken algorithm.
Injection
Untrusted input interpreted as a command, classically SQL injection. Use parameterised queries everywhere and never concatenate user input into a query string. Validate and sanitise input, and apply the same caution to NoSQL, command, and template injection. This is also why we treat the N+1 and raw-query temptations in our database guide with care.
Insecure design
Flaws baked into the architecture rather than the code. Threat-model features before building them, and design controls like rate limiting and segregation of duties from the start. You cannot patch your way out of a fundamentally insecure design, which is the whole premise of zero trust.
Security misconfiguration
Default credentials, verbose error messages, unnecessary features left on. Harden every environment, disable what you do not use, keep error output generic in production, and automate configuration so it is consistent and reviewable rather than hand-tuned per server.
Vulnerable and outdated components
Most applications are mostly other people's code. Track your dependencies, scan them automatically, and patch known vulnerabilities promptly. This category bleeds directly into supply chain security, which deserves its own attention.
Build it into the process, not the audit
The teams that consistently avoid these vulnerabilities are not the ones that run a security audit once a year. They are the ones who have folded the defences into everyday development so the secure path is the easy path. Parameterised queries are the default because the data layer makes them so. Authorisation checks are a standard part of every endpoint template. Dependency scanning runs on every change without anyone thinking about it. When prevention lives in tooling, conventions, and review rather than in a checklist someone remembers under deadline pressure, the whole class of risk shrinks. Treat the OWASP list not as an exam to pass at release time but as a set of habits to encode into how the team writes code every day, so that doing the right thing requires no extra discipline.
The rest, briefly
Round out your defences against the remaining categories: enforce strong authentication and session management to prevent identification failures; verify the integrity of code and data in your pipeline; log and monitor security events so breaches are detected, not discovered months later; and validate any server-side request that uses a user-supplied URL to prevent SSRF. None of these are exotic. They are disciplines applied consistently, which is exactly what our security and QA team builds into client systems before launch.