Secure Code Review Checklist for Developers

Writing secure code is non-negotiable in modern software development. A single vulnerability can lead to data breaches, system downtime, and a loss of user trust. The simplest, most effective fix is to catch these issues before they reach production. This is accomplished through a rigorous code review process, guided by a secure code review checklist.

A secure code review checklist is a structured set of guidelines and verification points used during the code review process. It ensures that developers consistently check for common security vulnerabilities and adhere to best practices. For instance, a checklist item might ask, "Is all user-supplied input validated and sanitized to prevent injection attacks (e.g., SQLi, XSS)?" 

This article provides a detailed guide to creating and using such a checklist, helping you build more resilient and trustworthy applications from the ground up. We will cover why a checklist is essential, how to prepare for a review, core items to include, and how to integrate automation to make the process efficient and repeatable.

Why Use a Secure Code Review Checklist?

Code quality and vulnerability assessment are two sides of the same coin. A checklist provides a systematic approach to both. It helps standardize the review process across your entire team, ensuring no critical security checks are overlooked. This is why we use a secure code review checklist.

The primary benefit is catching security issues early in the development lifecycle. Fixing a vulnerability during development is significantly less costly and time-consuming than patching it in production. According to a report by the Systems Sciences Institute at IBM, a bug found in production is six times more expensive to fix than one found during design and implementation.

Organizations like the Open Web Application Security Project (OWASP) provide extensive community-vetted resources that codify decades of security wisdom. A checklist helps you put this wisdom into practice. Even if the checklist items seem obvious, the act of using one frames the reviewer's mindset, focusing their attention specifically on security concerns. This focus alone significantly increases the likelihood of detecting vulnerabilities that might otherwise be missed.

• Standardization: Ensures every piece of code gets the same security scrutiny.

• Efficiency: Guides reviewers to the most critical areas quickly.

• Early Detection: Finds and fixes flaws before they become major problems.

• Knowledge Sharing: Acts as a teaching tool for junior developers.

Preparing Your Secure Code Review

A successful review starts before you look at a single line of code. Proper preparation ensures your efforts are focused and effective. Without a plan, reviews can become unstructured and miss critical risks.

Threat Modeling First

Before reviewing code, you must understand the application's potential threats. Threat modeling is a process where you identify security risks and potential vulnerabilities.

Ask questions like:

• Where does the application handle sensitive data?

• What are the entry points for user input?

• How do different components authenticate with each other?

• What external systems does the application trust?

This analysis helps you pinpoint high-risk areas of the codebase architecture that demand the most attention.

Define Objectives

Clarify the goals of the review. Are you hunting for specific bugs, verifying compliance with a security standard, or improving overall code quality? Defining your objectives helps focus the review and measure its success.

Set Scope

You do not have to review the entire codebase at once. Start with the most critical and high-risk code segments identified during threat modeling.

Focus initial efforts on:

• Authentication and Authorization Logic: Code that handles user logins and permissions.

• Session Management: Functions that create and manage user sessions.

• Data Encryption Routines: Any code that encrypts or decrypts sensitive information.

• Input Handling: Components that process data from users or external systems.

Gather the Right Tools and People

Assemble a review team with a good mix of skills. Include the developer who wrote the code, a security-minded developer, and, if possible, a dedicated security professional. This combination of perspectives provides a more thorough assessment.

Equip the team with the proper tools, including access to the project's documentation and specialized software. For instance, static analysis tools can automatically scan for vulnerabilities. For threat modeling, you might use OWASP Threat Dragon, and for automation, a platform like GitHub Actions can integrate security checks directly into the workflow.

Core Secure Code Review Checklist Items

This section contains the fundamental items that should be part of any review. Each one targets a common area where security vulnerabilities appear.

1) Input Validation

Attackers exploit applications by sending malicious or unexpected input. Proper input validation is your first line of defense.

• Validate on the Server Side: Never trust client-side validation alone. Attackers can easily bypass it. Always re-validate all inputs on the server.

• Classify Data: Separate data into trusted (from internal systems) and untrusted (from users or external APIs) sources. Scrutinize all untrusted data.

• Centralize Routines: Create and use a single, well-tested library for all input validation. This avoids duplicated effort and inconsistent logic.

• Canonicalize Inputs: Convert all input into a standard, simplified form before processing. For example, enforce UTF-8 encoding to prevent encoding-based attacks.

2) Output Encoding

Output encoding prevents attackers from injecting malicious scripts into the content sent to a user's browser. This is the primary defense against Cross-Site Scripting (XSS).

• Encode on the Server: Always perform output encoding on the server, just before sending it to the client.

• Use Context-Aware Encoding: The method of encoding depends on where the data will be placed. Use specific routines for HTML bodies, HTML attributes, JavaScript, and CSS.

• Utilize Safe Libraries: Employ well-tested libraries provided by your framework to handle encoding. Avoid writing your own encoding functions.

3) Authentication & Authorization

Authentication confirms a user's identity, while authorization determines what they are allowed to do. Flaws in these areas can give attackers complete control.

• Enforce on the Server: All authentication and authorization checks must occur on the server.

• Use Tested Services: Whenever possible, integrate with established identity providers or use your framework's built-in authentication mechanisms.

• Centralize Logic: Place all authorization checks in a single, reusable location to ensure consistency.

• Hash and Salt Passwords: Never store passwords in plain text. Use a strong, adaptive hashing algorithm like Argon2 or bcrypt with a unique salt for each user.

• Use Vague Error Messages: On login pages, use generic messages like "Invalid username or password." Specific messages ("User not found") help attackers identify valid accounts.

• Secure External Credentials: Protect API keys, database credentials, and other secrets. Store them outside of your codebase using a secrets management tool.

4) Error Handling & Logging

Proper error handling prevents your application from leaking sensitive information when something goes wrong.

• Avoid Sensitive Data in Errors: Error messages shown to users should never contain stack traces, database queries, or other internal system details.

• Log Sufficient Context: Your internal logs should contain enough information for debugging, such as a timestamp, the affected user ID (if applicable), and the error details.

• Do Not Log Secrets: Ensure that passwords, API keys, session tokens, and other sensitive data are never written to logs.

5) Data Encryption

Data must be protected both when it is stored (at rest) and when it is being transmitted (in transit).

• Encrypt Data in Transit: Use Transport Layer Security (TLS) 1.2 or higher for all communication between the client and server.

• Encrypt Data at Rest: Protect sensitive data stored in databases, files, or backups.

• Use Proven Standards: Implement strong, industry-accepted encryption algorithms like AES-256. For databases, use features like Transparent Data Encryption (TDE) or column-level encryption for the most sensitive fields.

6) Session Management & Access Controls

Once a user is authenticated, their session must be managed securely. Access controls ensure users can only perform actions they are authorized for.

• Secure Session Tokens: Generate long, random, and unpredictable session identifiers. Do not include any sensitive information within the token itself.

• Expire Sessions Properly: Sessions should time out after a reasonable period of inactivity. Provide users with a clear log-out function that invalidates the session on the server.

• Guard Cookies: Set the Secure and HttpOnly flags on session cookies. This prevents them from being sent over unencrypted connections or accessed by client-side scripts.

• Enforce Least Privilege: Users and system components should only have the minimum permissions necessary to perform their functions.

7) Dependency Management

Modern applications are built on a foundation of third-party libraries and frameworks. A vulnerability in one of these dependencies is a vulnerability in your application.

• Use Software Composition Analysis (SCA) Tools: These tools scan your project to identify third-party components with known vulnerabilities.

• Keep Dependencies Updated: Regularly update your dependencies to their latest stable versions. Studies from organizations like Snyk regularly show that a majority of open-source vulnerabilities have fixes available. A 2025 Snyk report showed projects using automated dependency checkers fix vulnerabilities 40% faster.

8) Logging & Monitoring

Secure logging and monitoring help you detect and respond to attacks in real-time.

• Track Suspicious Activity: Log security-sensitive events such as failed login attempts, access-denied errors, and changes to permissions.

• Monitor Logs: Use automated tools to monitor logs for patterns that could indicate an attack. Set up alerts for high-priority events.

• Protect Your Logs: Ensure that log files are protected from unauthorized access or modification.

9) Threat Modeling

During the review, continuously refer back to your threat model. This helps maintain focus on the most likely attack vectors.

• Review Data Flows: Trace how data moves through the application.

• Validate Trust Boundaries: Pay close attention to points where the application interacts with external systems or receives user input.

• Question Assumptions: Could an attacker manipulate this data flow? Could they inject code or bypass a security control?

10) Code Readability & Secure Coding Standards

Clean, readable code is easier to secure. Ambiguous or overly complex logic can hide subtle security flaws.

• Write Clear Code: Use meaningful variable names, add comments where necessary, and keep functions short and focused.

• Use Coding Standards: Adhere to established secure coding standards for your language. Some great resources are the OWASP Secure Coding Practices, the SEI CERT Coding Standards, and language-specific guides.

11) Secure Data Storage

How and where you store sensitive data is critical. This goes beyond just encrypting the database.

• Protect Backups: Ensure that database backups are encrypted and stored in a secure location with restricted access.

• Sanitize Data: When using production data in testing or development environments, make sure to sanitize it to remove any real user information.

• Limit Data Retention: Only store sensitive data for as long as it is absolutely necessary. Implement and follow a clear data retention policy.

Automated Tools to Boost Your Checklist

Manual reviews are essential for understanding context and business logic, but they can be slow and prone to human error. For smaller teams, free and open-source tools like SonarQube, Snyk, and Semgrep perfectly complement a manual secure code review checklist by catching common issues quickly and consistently.

Integrate SAST and SCA into CI/CD

Integrate Static Application Security Testing (SAST) and Software Composition Analysis (SCA) tools directly into your Continuous Integration/Continuous Deployment (CI/CD) pipeline. This automates the initial security scan on every code commit.

• SAST Tools: These tools analyze your source code without executing it. They are excellent at finding vulnerabilities like SQL injection, buffer overflows, and insecure configurations.

• SCA Tools: These tools identify all the open-source libraries in your codebase and check them against a database of known vulnerabilities.

Configure Security-Focused Rules

Configure your automated tools to enforce specific security rules tied to standards like OWASP Top 10 or the SEI CERT standards. This ensures that the automated checks are directly connected to your security requirements.

Popular Static Analysis Tools

Several tools can help automate parts of your review:

• PVS-Studio: A static analyzer for C, C++, C#, and Java code.

• Semgrep: A fast, open-source static analysis tool that supports many languages and allows for custom rules.

• SonarQube: An open-platform to manage code quality, which includes security analysis features.

Running The Review

With your preparation complete and checklist in hand, it is time to conduct the review. A structured approach makes the process more efficient and less draining for the participants.

Timebox Your Sessions

Limit each review session to about 60-90 minutes. Longer sessions can lead to fatigue and reduced focus, making it more likely that reviewers will miss important issues. It is better to have multiple short, focused sessions than one long, exhaustive one.

Apply the Checklist Systematically

Work through your checklist steadily. Start with the high-risk areas you identified during threat modeling. Use a combination of automated tools and manual inspection.

1. Run Automated Scans First: Let SAST and SCA tools perform an initial pass to catch low-hanging fruit.

2. Manually Inspect High-Risk Code: Use your expertise and the checklist to examine authentication, authorization, and data handling logic.

3. Validate Business Logic: Check for flaws in the application's logic that an automated tool would miss.

Track Metrics for Improvement

To make your process repeatable and measurable, track key metrics.

Keeping Your Process Up to Date

Security is not a one-time activity. The threat environment is constantly changing, and your review process must adapt. An effective secure code review checklist is a living document.

Update for New Threats

Regularly review and update your checklist to include checks for new types of vulnerabilities. Stay informed by following security publications from organizations like NIST and OWASP. When a new major vulnerability is disclosed (like Log4Shell), update your checklist to include specific checks for it.

Build a Security-First Mindset

The ultimate goal is to create a team where everyone thinks about security. Use the code review process as an educational opportunity. When you find a vulnerability, explain the risk and the correct way to fix it. This continuous training builds a stronger, more security-aware engineering team.

Sample “Starter” Checklist

Here is a starter secure code review checklist based on the principles discussed. You can use this as a foundation and customize it for your specific tech stack and application. This is structured in a format you can use in a GitHub pull request template.

For a more detailed baseline, the OWASP Code Review Guide and the associated Quick Reference Guide are excellent resources.

Input Validation

• [Critical] Is the application protected against injection attacks (SQLi, XSS, Command Injection)?

• [Critical] Is all untrusted input validated on the server side?

• [High] Is input checked for length, type, and format?

• [Medium] Is a centralized input validation routine used?

Authentication & Authorization

• [Critical] Are all sensitive endpoints protected with server-side authentication checks?

• [Critical] Are passwords hashed using a strong, salted algorithm (e.g., Argon2, bcrypt)?

• [Critical] Are authorization checks performed based on the user's role and permissions, not on incoming parameters?

• [High] Are account lockout mechanisms in place to prevent brute-force attacks?

• [High] Does the principle of least privilege apply to all user roles?

Session Management

• [Critical] Are session tokens generated with a cryptographically secure random number generator?

• [High] Are session cookies configured with the HttpOnly and Secure flags?

• [High] Is there a secure log-out function that invalidates the session on the server?

• [Medium] Do sessions time out after a reasonable period of inactivity?

Data Handling & Encryption

• [Critical] Is all sensitive data encrypted in transit using TLS 1.2+?

• [High] Is sensitive data encrypted at rest in the database and in backups?

• [High] Are industry-standard encryption algorithms (e.g., AES-256) used?

• [Medium] Are sensitive data or system details avoided in error messages?

Dependency Management

• [High] Has an SCA tool been run to check for vulnerable third-party libraries?

• [High] Are all dependencies up to their latest secure versions?

Logging & Monitoring

• [Critical] Are secrets (passwords, API keys) excluded from all logs?

• [Medium] Are security-relevant events (e.g., failed logins, access denials) logged?

Conclusion

Building secure software requires a deliberate and systematic effort. This is why your team needs a secure code review checklist. It provides structure, consistency, and a security-first focus to your development process. It transforms code review from a simple bug hunt into a powerful defense against attacks.

For the best results, combine the discipline of a powerful secure code review checklist with automated tools and the contextual understanding that only human reviewers can provide. This layered approach ensures you catch a wide range of issues, from simple mistakes to complex logic flaws. Begin integrating these principles and build your own secure code review checklist today. Your future self will thank you for the secure and resilient applications you create.

FAQs

1) What are the 7 steps to review code?

A standard secure code review process involves seven steps:

1. Define review goals and scope.

2. Gather the code and related artifacts.

3. Run automated SAST/SCA tools for an initial scan.

4. Perform a manual review using a checklist, focusing on high-risk areas.

5. Document all findings clearly with actionable steps.

6. Prioritize the documented issues based on risk.

7. Remediate the issues and verify the fixes.

2) How to perform a secure code review?

To perform a secure code review, you should first define your objectives and scope, focusing on high-risk application areas. Then, use a checklist to guide your manual inspection, and supplement your review with SAST and SCA tools. Document your findings and follow up to ensure fixes are correctly implemented.

3) What is a code review checklist?

A secure code review checklist is a structured list of items that guides a reviewer. It ensures consistent and thorough coverage of critical security areas like input validation, authentication, and encryption, helping to prevent common vulnerabilities and avoid gaps in the review process.

4) What are SAST tools during code review?

SAST stands for Static Application Security Testing. These tools automatically scan an application's source code for known vulnerability patterns without running the code. Tools like PVS-Studio, Semgrep, or SonarQube can find potential issues such as SQL injection, buffer overflows, and insecure coding patterns early in development.

5) How long should a secure code review take per 1,000 LOC?

There isn't a strict time rule, as the duration depends on several factors. However, a general industry guideline for a manual review is between 1 to 4 hours per 1,000 lines of code (LOC).

Factors that influence this timing include:

• Code Complexity: Complex business logic or convoluted code will take longer to analyze than simple, straightforward code.

• Reviewer's Experience: A seasoned security professional will often be faster and more effective than someone new to code review.

• Programming Language: Some languages and frameworks have more inherent security risks and require more scrutiny.

• Scope and Depth: A quick check for the OWASP Top 10 vulnerabilities is much faster than a deep, architectural security review.