Authentication Bypass

Authentication Bypass occurs when the code path taken by a request differs from what the developer assumed — typically because an edge case in routing, middleware ordering, or header handling allows an attacker to skip the authentication check entirely. The Next.js middleware bypass (CVE-2025-29927) is a textbook example: a specific request header caused the middleware to skip its own auth check.

These vulnerabilities are particularly insidious in code review because the authentication logic looks correct when read in isolation. The vulnerability only becomes visible when you also consider how the framework routes requests, what headers it normalizes, and whether there are any paths through the middleware chain that do not pass through the check. This is the kind of cross-cutting analysis that is easy to miss in a line-by-line diff review.

PullLight maps the request flow for every new route added in a PR and verifies that authentication middleware is applied consistently — including edge cases for trailing slashes, URL encoding, and framework-specific header handling that is known to cause bypass patterns.