Secure Code Review
OWASP Best Practices
Amartya Jha
• 19 June 2025
“What could go wrong if this gets abused?”
1. Code Review Is Broken, Here's What OWASP Wants You to Fix
Yup, code review is a ritual now.
Every team does it. Every PR has a few comments.
But here’s the kicker: most of it completely misses the point when it comes to security.
What OWASP is saying, and pretty loudly in its Code Review Guide PDF, is that you can’t “hack yourself secure.”
Security doesn’t magically show up at the end of the cycle.
And no, your pen test report isn’t going to catch the messy assumptions quietly hiding in your business logic.
If you wait till production to find out your session handling is broken or your access controls are too loose… It’s already expensive, not just in dev time, but in credibility.
OWASP’s message is blunt, but fair:
👉 We’re fighting an asymmetric battle. Attackers have infinite time. You don’t.
So your only real advantage is to catch things early, during code review.
And yeah, that means rethinking what you’re actually looking for during a review.
It’s not just “does the code work?”
It’s “could this be abused?”,
“Does this respect the context it’s running in?”,
And “are we exposing something we shouldn’t?”
You might think you’re being thorough, but if you're not reviewing through that lens, OWASP says you’re probably missing the real threats.
And they’re not wrong.
2. Secure Code Review vs. Regular Code Review
If you’ve ever done a code review and thought “looks clean, good to go”, yes, we are the same.
But OWASP wants you to pause and ask: “Clean for whom?”
Because code that’s clean for functionality might still be a minefield for security.
And that’s the key difference OWASP draws:
👉 Regular code review is about how the code works.
👉 Secure code review is about how the code could break, especially in the wrong hands.
Let’s break it down the way OWASP does in their guide.
Regular Code Review: The Baseline
OWASP explains this using the Capability Maturity Model (CMM).
Most dev orgs hit Level 2 or 3 before they even start doing consistent reviews.
At this stage, teams usually:
Catch logic bugs
Enforce style guides or best practices
Review for maintainability and functionality
And that’s great. You’re checking if the code does what it’s supposed to.
But what you're not doing (yet) is asking:
Does this create a new attack surface?
Is this logic safe under misuse?
Could a bad actor turn this into a breach?
That’s where secure code review enters.
Secure Code Review: The Upgrade
Now, here’s what OWASP’s Code Review Guidelines add:
Secure code review brings risk into the conversation. Not every line of code is equal, and OWASP makes that clear.
So instead of just checking the "what", you’re reviewing for:
Risk levels tied to the module or feature
Are security controls present, consistent, and effective?
Contextual impact: What happens if this code fails under attack?
This means:
High-risk areas (auth, session mgmt, payments) get deeper scrutiny
Reviewers need domain understanding, not just syntax knowledge
Business implications start to shape how deeply you review
And OWASP calls this out directly:
“Secure code review is an enhancement to the standard practice, where security standards drive the decision-making.”
In simpler terms?
You don’t just ask: Does this work?
You ask: Could this get us burned?
Why This Matters in Real Life
OWASP’s not saying you need a military-grade review for every CSS tweak. In fact, they say the opposite.
Smaller orgs might start with one person doing light checks. Larger teams might assign reviewers based on the risk profile of the code. (They even suggest having different repositories or access levels for sensitive modules.)
What matters is that you’re intentional about how deeply you go, based on the impact of what’s being changed.
They also emphasize one more thing:
Secure review isn’t about gatekeeping or slowing people down.
It’s about baking security into your existing dev process, so you don’t have to patch it later, when it’s more painful (and expensive).
So we learned in the previous section that secure code review isn’t just a stricter version of regular review, it’s a shift in how you look at code entirely. You're not just scanning for bugs; you're trying to understand risk in context.
And that brings us to something OWASP repeats again and again in their Code Review Guide PDF:
👉 Context is everything.
Without it, you’re just checking boxes, and probably checking the wrong ones.
3. The Mindset Shift: Context Beats Checklists
OWASP doesn’t say “don’t use checklists,” they suggest them as helpful tools.
But what they really drive home is this:
> If you don’t know what the code is meant to do, you have no way of knowing if it’s secure.
You can’t just skim a file and spot vulnerabilities in isolation.
You need to know:
What is this module for?
Who’s using it?
What data flows through it?
What happens if it fails?
What does “secure” even mean in this business context?
Yup, that’s more thinking.
But it’s also where the real value of code review comes from, especially when security’s involved.
OWASP gives a few good reasons why this matters:
1. Vulnerabilities aren’t always obvious
You might look at a piece of code and think: “Looks clean, good logic, follows best practices.”
But that same code might:
Expose sensitive data if accessed by the wrong user
Bypass auth checks under certain edge conditions
Fail silently when a critical validation is skipped
And you wouldn’t catch that just by reading line-by-line, you’d need to understand how the system works as a whole.
2. Context drives priority
OWASP also says something teams often overlook:
Not all code needs the same depth of review.
If the change touches:
Authentication
Access control
Session management
Payment workflows
Personally identifiable information (PII)
…then that’s a high-context, high-risk area.
You dig deeper. Maybe pull in another reviewer. Maybe pause and ask a few more questions.
But if it’s a UI refactor with no business logic changes?
Lighter touch. Less scrutiny.
The point OWASP makes is: your review depth should match the risk, and the only way to know the risk is to understand the context.
3. You’re not reviewing code. You’re reviewing decisions.
4. Who Should Do the Review? How Teams Can Actually Pull This Off
In smaller teams, secure code review might start off informal, maybe one or two folks who know the system well and care about security. That’s fine.
But as the system grows, the codebase gets more complex, and the stakes get higher, you need a more reliable structure.
Here’s how this actually works in the field, straight from the guide:
1. The SME model
For sensitive areas, like authentication, crypto, or anything that touches user trust, reviews are ideally done by someone with subject matter expertise.
And yeah, sometimes that’s not the developer who wrote the code.
This doesn’t mean every team needs a full-time security engineer.
It can just mean looping in someone who’s handled this before, or is familiar with the risks involved.
When that’s not available, pairing the dev with someone who has domain experience works well too.
The key is: knowledge of the security domain being touched is non-negotiable. Otherwise, you’re just reviewing syntax, not safety.
2. Review scope matters
The guide makes a clear point: Secure review can happen at multiple levels.
Reviewing individual code changes
Reviewing entire modules
Reviewing based on functionality or feature sets
Reviewing based on identified vulnerabilities or historical issues
Each level requires a slightly different lens, and possibly a different person doing the review.
So it’s not just about who’s reviewing.
It’s about what they’re reviewing and how well that matches their context.
3. Making it scalable
Teams can’t stop shipping every time a secure review is needed.
One thing that helps is dividing up responsibility based on areas of expertise, especially for large codebases. Some teams assign module owners. Others build small “security satellites” inside dev teams.
Another way is to maintain a list of code areas that require mandatory review from specific people, things like access control modules, payment processors, and login systems.
That way, people aren’t guessing who should review what. It’s clear, it’s scoped, and it doesn’t rely on memory.
4. When and how to assign reviewers
It’s often better to plan review assignments at the start of the task, not at the end.
This way, the person doing the secure review can get familiar with the feature’s intent, and not just the final diff.
And if the reviewer was involved in the early threat modeling or design discussions? Even better.
They’ll have the full context, and the thing we’ve already established is the most important piece.
Code review is a team effort. But secure code review?
That needs the right eyes on the right things, with enough context to spot what could go wrong.
Get that part right, and the rest becomes a lot easier to trust.
So once you know who’s reviewing what, and you’ve got the right eyes on the right modules, the next question is:
What exactly are we supposed to look for?
And that’s where the OWASP guide gets really practical.
It doesn’t throw random lists at you.
Instead, it breaks reviews into distinct types, based on what stage the code is in, what kind of decisions were made, and how those decisions affect your overall risk.
5. The Types of Code Reviews, And What You’re Actually Looking For
Now this is where it gets interesting.
Secure code review isn’t just about reading source files and hoping a vulnerability pops out.
The OWASP Code Review Guide gives you a breakdown of different kinds of reviews, depending on what you're trying to catch.
Let’s walk through the ones that matter most.
1. Design / API Review
Purpose: Catch architectural flaws before they become implementation nightmares.
At this point, you’re not reading code; you’re reviewing how the system is supposed to work.
You look at:
How data flows across modules
Where trust boundaries are (and how they’re protected)
How external services and APIs are integrated
What authentication and authorization models are planned
This is where a lot of security debt gets introduced, silently.
Bad design choices here lead to insecure code later, even if the code itself “works.”
And yup, this kind of review is often skipped because “there’s no code yet.”
But it’s one of the most impactful ones if you actually do it.
1. Code Review (Line-by-line)
Purpose: Find logic flaws, unsafe functions, and violations of security standards.
This is the classic one.
You’re digging into source files, and you’re looking for:
Input validation issues
Missing error handling
Bad cryptographic practices
Business logic flaws
Inconsistent access control
This is where secure coding standards come into play.
If your org doesn’t have one yet, the review becomes inconsistent, because everyone’s judging code based on different ideas of what “secure” means.
Also, this is where most tools (like SAST) try to help, but more on that later.
2. Integration Review
Purpose: Check how secure code interacts with the rest of the system.
Let’s say you’ve got a perfectly written module.
No bugs. Great validation. Secure functions.
But then it integrates with something that breaks all of that.
Integration reviews are where you look at:
How data is passed between services
Whether controls are enforced consistently across boundaries
If there's trust placed on incoming data that shouldn't be trusted
Basically, this is where security assumptions can quietly fail, and they often do.
3. Testing Review
Purpose: Make sure that what you’ve reviewed is also being validated by tests.
Secure code review doesn’t stop at “the code looks fine.”
You also want to check:
Are there test cases for security edge conditions?
Do tests verify that access controls actually block unauthorized use?
Are failures handled gracefully, or do they expose sensitive info?
You don’t need full-blown threat modeling tied into your test suite (yet), but some of these reviews catch the moment where people write tests that only check happy paths, and totally miss misuse scenarios.
We’ve already walked through what to look for and how different types of secure reviews work.
But there’s still one big question every team runs into:
When should the review actually happen?
Because let’s be real, if it always happens after the code is merged (or worse, after it’s in prod), you’re not reviewing, you’re just cleaning up.
And the OWASP Code Review Guide makes that painfully clear.
6. When to Review Code, Pre-Commit, Post-Commit, or Audit Style?
So here’s the deal.
Secure code review isn’t tied to one fixed point in time.
Depending on your team’s structure, maturity, and speed, there are actually three main review timings.
And yup, each one has its pros, cons, and trade-offs.
1. Pre-Commit Review
Review before the code even lands in the repo.
This is the most proactive type, and often the most lightweight.
Usually, the developer who wrote the code walks another dev through the change, or the reviewer checks the patch before it’s committed.
This works best when:
The code is small and focused
The change is sensitive (think auth, sessions, payments)
You want to catch issues before they even hit the CI/CD pipeline
This kind of early review helps catch architectural assumptions or unsafe patterns before they get baked in.
It’s also super effective when paired with design discussions, you catch both design and code flaws in one go.
2. Post-Commit Review
Code gets merged, and review happens right after.
This is probably the most common style in fast-moving teams.
The review happens either:
Before the release (on a separate branch), or
After the change is live, but before too much builds on top of it
It’s flexible, but also a bit reactive.
You get less “design phase” context, but it’s still early enough to catch and fix things without major rework.
The guide highlights this as useful for routine changes or for scanning new code against known security standards.
Just don’t let this turn into “we’ll review it later, promise”, because later usually never comes.
3. Audit Review
The deep dive, done after the code is deployed or released.
This is where things get formal.
Audit-style reviews are:
Structured
Systematic
Usually tied to compliance, risk assessment, or major incidents
They cover larger chunks of code, often across modules or services.
And they’re great for finding issues that slipped through the cracks.
But they’re also time-consuming, and if this is your only kind of review, you’re probably catching things too late.
The OWASP guide makes a point: audit reviews shouldn’t replace secure code reviews in the SDLC; they should complement them.
So… what’s the right choice?
There isn’t one.
But the guide makes it clear: secure code review should be baked into your process, not stapled on at the end.
A mix often works best:
Pre-commit for sensitive changes
Post-commit for routine PRs
Audit reviews are quarterly or after big releases
The earlier you catch the risk, the cheaper and safer it is to fix.
And that’s kind of the whole point.
Tools That Help, And Where They Usually Fall Short
So now we’ve got timing, reviewers, and review types covered.
Naturally, the next thing teams ask is, Can we automate this?
Short answer: yes, but don’t stop there.
The OWASP Code Review Guide doesn’t dismiss tools. In fact, it lists a bunch of categories that can seriously level up your secure review process.
But it also makes one thing very clear:
No tool replaces human judgment.
Let’s walk through what the guide actually recommends and what to watch out for.
1. Static Code Analyzers (SAST)
These are the go-to tools for most dev teams.
They scan your codebase without executing it, looking for common patterns like:
SQL injection
XSS risks
Unsafe functions
Misuse of APIs
They’re fast, can be integrated into CI/CD, and flag a lot of known issues.
But here’s the catch: They’re only as smart as their rule set.
OWASP points out that SAST tools often:
Generate false positives
Miss context-specific logic issues
Struggle with custom frameworks or business logic flaws
So yea, great for surface-level hygiene, but don’t expect deep logic insight.
2. Dynamic Analysis Tools (DAST)
These are the “let’s run it and see what breaks” kind.
DAST tools test your running app by simulating external attacks, checking for things like:
Input validation flaws
Misconfigured security headers
Broken authentication flows
They’re super useful for catching real-world exposure.
But they’re reactive; they can only find what’s already deployed.
So if you're relying only on DAST to catch bugs, you're probably catching them later than you should.
3. Code Coverage & Diff Tools
These help you measure:
Which parts of the code have changed
Which parts are being tested
What needs fresh review
They’re not security tools, strictly speaking, but OWASP includes them because they’re crucial for review planning.
If you don’t know what changed, you can’t know what to review.
4. Threat Modeling Tools
This one’s more for design and early planning phases.
Some tools help you:
Map out components and data flows
Identify trust boundaries
Predict potential abuse paths
Used right, these tools help shape where your secure code reviews need to go deep, especially in high-risk modules.
But again, they guide the humans. They don’t do the review for you.
So… should you use tools?
Absolutely. OWASP’s view is pretty balanced here:
Tools can scale your review process.
But tools that just spit out alerts without context can easily be ignored or misused.
So, the smart move?
Use SAST/DAST to flag the obvious stuff
Use coverage tools to focus your review effort
Use threat models to prioritize what really matters
Then… bring in humans to do the thinking
Because no tool knows your app, your business logic, or your edge cases better than your team does.
(Yes, we’re working on helping CodeAnt.ai get really close.)
Wait, what’s CodeAnt.ai?
It’s your AI-powered reviewer that actually understands the context behind your code changes.
We built it for teams who were tired of sifting through noisy scans and vague alerts.
With CodeAnt.ai, you get:
A clean, reviewer-style dashboard
OWASP issues flagged and grouped by severity, risk, and code context
Feedback on every pull request, from security to secret detection
And real summaries, not just diffs
Here’s the fun part:
We just raised $2 million to help dev teams cut code review time and bugs by over 50%, and we’re just getting started.
Here is a normal repository dashboard as it looks. And you will see below how OWASP issues are captured inside CodeAnt.
👇 Here’s how CodeAnt works, showing you exactly how we surface OWASP-mapped issues and help you act on them.
No clutter. No false positives.
Just what you need to fix, and why.
Making It Stick: Building a Real Secure Code Review Culture
At the end of the day, tools are nice. Processes help.
But if secure code review always feels like “extra work,” no one will do it well, or at all.
The OWASP guide finishes strong here. It doesn’t just list technical best practices.
It reminds us that secure review only works if it becomes part of the team’s mindset.
Let’s break down what that really means.
1. Make security a shared responsibility
If secure review is only “the security team’s job,” you’ve already lost.
The guide stresses that all developers, not just AppSec, should be involved in the review process.
Why?
Because the people writing the code understand the logic and intent better than anyone.
If they also understand how attackers think? That’s where strong security begins.
And it’s not about scaring people.
It’s about showing that secure coding is just… good engineering.
2. Integrate review into the SDLC
The guide’s advice here is super practical:
Secure review should happen at multiple stages, from design to deployment
Make it part of existing workflows, not a last-minute blocker
Use code ownership to assign review responsibility where it makes sense
If your process supports code reviews, you’re already halfway there.
The trick is: add security without adding friction.
Keep things lean. Keep them real.
3. Prioritize based on risk
This one’s easy to forget.
Not all code needs the same level of scrutiny.
The guide encourages teams to:
Focus deep reviews on high-risk areas (auth, payments, data handling)
Use lighter checks for low-risk, low-impact modules
Create a rough risk profile so devs know when to slow down and zoom in
This makes the process sustainable; you’re not reviewing everything at the same intensity.
4. Support the reviewers
Secure code reviewers need context, time, and access to the right resources.
The guide points out that:
Reviewers should be trained on both the app and secure coding practices
They should know where to find threat models, security policies, and past incidents
They should feel safe calling out concerns, even if it slows a release
If your reviewers are rushed, overworked, or unsure of what matters, they’ll miss things. Simple as that.
5. Build feedback loops
The most resilient teams?
They treat reviews as a learning tool, not just a filter.
The OWASP PDF recommends:
Using review findings to improve coding guidelines
Tracking recurring issues to update checklists and patterns
Sharing lessons across teams, not just fixing and forgetting
That way, each review doesn’t just fix code.
It levels up everyone involved.
