Pentesting Next.js Server Actions

Next.js server actions are tricky to analyze during penetration tests because they appear as POST requests with opaque hash identifiers. The NextjsServerActionAnalyzer Burp extension helps by mapping these hashes to understandable function names when productionBrowserSourceMaps are enabled. This extension leverages the fact that minified JavaScript files contain mappings between action hashes and their corresponding function names. It automatically scans proxy history for JavaScript chunks, extracts these mappings, and creates a clear association between hashes and function names. Instead of tracking changing hash IDs, the extension focuses on constant function names, ensuring accurate identification even across different application builds. A powerful feature converts unused actions into testable requests within Burp, simplifying the testing process. In a recent assessment, the extension successfully mapped numerous server action hashes to their function names, improving test clarity. This allowed testers to easily identify and test functions like `updateUserProfile()` and `fetchReportData()`. The mapping enabled the discovery of unused server actions, which could then be targeted for testing. This approach allows for more efficient and focused security testing in Next.js applications. The extension ultimately transforms the way testers approach Next.js server action analysis. The extension provides a better understanding of application behavior.