A codebase-wide review is a security examination of an entire software project, not just the newest patch or pull request. It looks for issues that may be spread across multiple files or modules, such as insecure data handling, weak authentication logic, unsafe dependencies, or inconsistent access checks.
This matters because many vulnerabilities are systemic rather than local. An attacker may exploit a flaw only when several components interact in a dangerous way, so reviewing only the latest change can miss the bigger picture. In defense, codebase-wide reviews help teams find legacy defects, repeated insecure patterns, and hidden trust boundaries that create risk across the application. They are often used alongside pre-commit scans and human review, since automated tools can surface suspicious patterns but still need context to judge whether a finding is truly exploitable.