What is a secure code review?

In software development, speed is often the priority. However, deploying rapidly is risky if that code introduces vulnerabilities that compromise user data or operational stability. This is where application security code review becomes essential. It is the process of auditing source code to identify security weaknesses, logical errors, and vulnerabilities before the application is deployed.

Unlike dynamic testing, which probes a running application, a code review looks at the blueprint of the software—the code itself. It allows teams to identify the root cause of a vulnerability rather than just its symptoms. By integrating these reviews into your workflow, you ensure that security is not a bottleneck at the end of the project but a continuous standard maintained throughout development.

The basics of a secure code review

A secure code review is a specialized task involving the manual or automated examination of an application's source code. The primary goal is to identify security flaws that attackers could exploit. This process looks for specific vulnerability patterns, such as those outlined in the OWASP Top 10, including injection flaws, broken authentication, and sensitive data exposure.

While automated tools are critical for speed and coverage, a comprehensive review often involves developer expertise. A human reviewer understands the context of the code, business logic, and complex data flows that automated scanners might miss. The ultimate objective is to ensure the code is robust, defensible, and adheres to the organization's security policies.

Source code review vs. secure code review

It is common to confuse a standard peer review with a security-focused review. While both involve examining code, their objectives and the "lens" through which the reviewer looks are fundamentally different.

A standard source code review is primarily concerned with the functionality and maintainability of the code. The reviewer asks questions like: "Does this code work?" "Is it efficient?" or "Does it follow our style guide?"

A secure code review assumes the code might work functionally but checks if it can be abused. The reviewer asks: "How could an attacker manipulate this input?" or "Does this function expose sensitive data?"

When to perform secure code reviews in the SDLC

Historically, security testing was a phase that occurred at the very end of the software development life cycle (SDLC). This "waterfall" approach meant that if a critical vulnerability was found, it required tearing down and rewriting significant portions of the application, leading to delays.

Today, industry best practices dictate that security code review should be done throughout the SDLC. This aligns with the philosophy of shifting left—moving security activities earlier in the development timeline.

The most critical time to perform these reviews is during the pull request (PR) or merge request phase. By treating the PR as a "gate," organizations ensure that no code enters the main branch without passing security checks. This implies that code auditing happens continuously, in small batches.

Key moments to trigger a review include:

• During coding: Using IDE extensions to catch issues in real time.
• At check-in: When code is committed to the repository.
• During the build: Automated scanners running within the CI/CD pipeline.
• Before major releases: A deep-dive manual review for critical features or high-risk modules.

What are the benefits of secure code review?

Implementing a robust review strategy offers advantages that extend beyond just "being secure." The benefits impact the bottom line, team culture, and product quality.

• Cost reduction: The cost of fixing a bug increases exponentially the later it is found. A security flaw identified during the coding phase might take ten minutes to fix. If that same flaw is found in production, it could cost thousands of dollars in remediation, patch deployment, and potential downtime.
• Compliance and risk management: For industries regulated by standards like PCI DSS, HIPAA, or GDPR, proving that you have a secure development process is often mandatory. Regular code reviews provide the audit trail necessary to demonstrate due diligence.
• Developer education: One of the most valuable benefits is knowledge transfer. When a developer receives feedback on a security vulnerability in their specific code, they learn how to avoid that mistake in the future. Over time, this raises the security skills of the entire engineering team.
• Reduced technical debt: Security vulnerabilities are a form of technical debt. By addressing them continuously, you maintain a higher level of code health, preventing a backlog of security tickets that can paralyze future feature development.

The OWASP secure code review process

The Open Web Application Security Project (OWASP) is the global standard-bearer for application security. The OWASP secure code review methodology provides a structured approach to auditing code, ensuring that reviews are consistent and thorough.

While the full guide is extensive, the process can be boiled down to an actionable workflow for development teams:

• Identify security objectives: Before reviewing, understand the application's risk profile. Is it handling credit card data? Does it face the public internet? The scrutiny level should match the risk.
• Threat modeling: Understand the architecture. Where are the "entry points" for data? Where are the "trust boundaries"? You cannot secure code if you don't understand how data flows through it.
• Automated scanning: Use tools to sweep the codebase first. Machines are better at finding missing semicolons or known vulnerable dependencies than humans.
• Manual analysis: This is the core of the OWASP methodology. Reviewers look for logic flaws that tools miss, such as broken access controls.
• Reporting and remediation: Findings must be documented clearly with reproduction steps and remediation advice. The process isn't complete until the fix is verified.

A secure code review checklist

To ensure consistency, teams should utilize a secure code review checklist. While every application is unique, the following categories cover the foundational elements of a secure application:

Input validation and data sanitization

• Is all input from untrusted sources (users, external APIs, files) validated?
• Are strict allow-lists used instead of block-lists?
• Is output encoded to prevent cross-site scripting (XSS)?
• Are SQL queries parameterized to prevent SQL injection?

Authentication and session management

• Are passwords hashed using strong algorithms (e.g., Argon2, bcrypt)?
• Is multi-factor authentication (MFA) enforced where necessary?
• Do sessions time out appropriately?
• Are session tokens invalidated upon logout?

Access control (authorization)

• Does the code verify that the user is authorized to perform the requested action?
• Are direct object references (IDOR) protected?
• Is the principle of least privilege applied to database connections and service accounts?

Cryptography and secrets management

• Has secrets detection been implemented to ensure no API keys, tokens, or passwords are hard-coded in the source code?
• Is data encrypted at rest and in transit (TLS)?
• Are weak cryptographic algorithms (e.g., MD5, SHA1) avoided?

Error handling and logging

• Do error messages avoid revealing sensitive stack traces or system details to users?
• Are security-critical events (logins, failed actions) logged?
• Is sensitive data (PII, passwords) excluded from logs?

Secure code review tools

Given the size of modern codebases, manual review alone is impossible. Teams must leverage a secure code review tool to scale their security efforts. These tools fall into several categories, each serving a different purpose in the review ecosystem.

• Static application security testing (SAST): SAST tools analyze source code at rest. They don't need the application to be running. They are excellent at finding coding errors, such as unpatched libraries or injection flaws, early in the SDLC. Because they look at the code, they can point to the exact line number where the issue exists.
• Dynamic application security testing (DAST): DAST tools attack the running application from the outside, mimicking a hacker. While not strictly a "code review" tool, they provide validation that the code is vulnerable in a runtime environment.
• Software composition analysis (SCA): Modern applications are built on open source libraries. SCA tools review your codebase not for your code, but for the open source components you have imported, checking them against databases of known vulnerabilities.

Automated security code review tools should be integrated directly into the CI/CD pipeline. However, remember that tools are meant to support the human reviewer, not replace them.

Key takeaways

• Different intent: Secure code review focuses on risk and exploitation, while source code review focuses on logic and maintenance.
• Start left: Perform security reviews throughout the SDLC, specifically at the pull request stage, to catch bugs when they are cheapest to fix.
• Hybrid approach: The most effective strategy combines automated security code review tools (for coverage and speed) with manual human review (for context and logic).
• Consistency matters: Use a standardized checklist (based on OWASP) to ensure no critical areas like authentication or input validation are overlooked.
• Continuous improvement: Use findings from reviews to educate developers, reducing the recurrence of similar vulnerabilities in the future.

How Sonar helps you build better software, faster

The challenge for many organizations is bridging the gap between knowing security is important and actually implementing it without slowing down development. Sonar provides a solution that integrates code quality and code security directly into your existing workflows. It adds an essential verification layer for all code. By offering actionable code intelligence, Sonar empowers developers to identify and fix issues regarding reliability, maintainability, and security before they ever reach production.

SonarQube acts as the industry standard for automated code review, providing an essential trust and verification layer for all code, across over 35 programming languages. Whether you are using SonarQube Server for self-managed control or SonarQube Cloud for seamless cloud DevOps integration, the platform analyzes your code against thousands of rules to catch complex vulnerabilities like injection flaws and broken access controls. Furthermore, SonarQube for IDE and SonarQube MCP Server brings this analysis directly into the IDEs, AI-native IDEs, and LLM based CLIs (such as Gemini CLI) , providing real-time feedback and automated fixes as code is being written, ensuring that security standards are met from the very first keystroke.

Crucially, Sonar addresses the modern challenge of AI-generated code. With features like AI Code Assurance, Sonar ensures that all code—whether written by a developer or generated by an AI assistant—is held to the same high standards of quality and security. This allows teams to confidently adopt AI tools to increase velocity without introducing hidden risks or technical debt, solving the engineering productivity paradox by verifying code health at scale. Essentially, Sonar is the trust and verification layer for all code.