Security Code Review - Catching Bugs Before Release

About 2 min read

Code review is a quality management practice in which source code written by one developer is inspected by another to find bugs, vulnerabilities, and design problems. According to research by IBM, code review can detect more defects than testing, with a defect removal rate reaching 60 to 90%. From a security perspective, a major strength is that human eyes can detect flaws in authorization logic and business-logic vulnerabilities that are difficult for automated tools to catch. As of 2025, the importance of code review is growing, including from the standpoint of verifying the security quality of code generated by code-completion tools such as GitHub Copilot.

Real-World Use Case

"During a pull request review, I found an API endpoint that was missing an authorization check. It was an IDOR (Insecure Direct Object Reference) vulnerability that let any authenticated user access another person's data, a pattern the SAST tool had failed to detect."

Reviewing from a Security Perspective

In a security code review, you focus on missing input validation, SQL injection and XSS vulnerability patterns, hardcoded credentials, and improper error handling (such as exposing stack traces). The OWASP Code Review Guide recommends prioritizing four areas for inspection: authentication, authorization, session management, and encryption.introductory books on code review (Amazon) offer a systematic way to learn.

How to Conduct It Effectively

The optimal amount of code to review in a single session is considered to be 200 to 400 lines; beyond that, concentration drops and oversights increase. Use a checklist for reviews and systematically verify items aligned with the principles of secure coding. Asynchronous reviews using tools, such as GitHub pull request reviews and GitLab merge request reviews, are mainstream, but synchronous reviews in a pair-programming style are also effective for complex logic. Protect access to your repository with a strong random password and set up branch protection rules that prevent merges without review approval.books on software quality (Amazon) are also a useful reference.