A code diff is a side-by-side view of changes between two versions of source code. It shows what was added, removed, or modified in a patch, making it easier to review a fix before it is merged into a branch or released.
In cybersecurity, diffs are critical because they reveal whether a patch really closes a vulnerability or accidentally introduces a new one. Defenders use diffs during code review, incident response, and secure release workflows to check for unsafe logic changes, missing input validation, broken access controls, or unexpected side effects. Attackers also study public diffs to spot newly introduced flaws, reverse-engineer security fixes, and race defenders by exploiting a weakness before every system is updated. Strong review of diffs, combined with testing and approval controls, helps organizations catch risky changes before they become production security problems.