fix: correct path traversal check to allow '...' in URL path segments#461
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mcollina merged 2 commits intofastify:mainfrom Mar 11, 2026
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Next.js catch-all routes like '[...slug]' appear percent-encoded as '%5B...slug%5D' in static chunk URLs. These contain '...' as a substring but are not path traversal and should not be rejected. See: fastify#460
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To start, I am only pushing up the test change. The unit test should fail. Once we've shown that, I will push up the fix. I just need a maintainer to approve the GHA workflow run. |
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go ahead and keep going with the implementation |
The previous check used includes('..') which incorrectly rejects URLs
containing '...' as part of a filename or route name, such as Next.js
catch-all routes like '[...slug]' (%5B...slug%5D when percent-encoded).
Replace with a targeted check that only flags '..' when it appears as a
complete path segment (surrounded by '/' or at a string boundary).
Fixes: fastify#460
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Pushed up the proposed fix. |
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Summary
Fixes #460
The path traversal check in
buildURLusesincludes('..')which incorrectly rejects URLs containing...(three dots) as part of a filename or route name, for example, Next.js catch-all routes like[...slug], which appear percent-encoded as%5B...slug%5Din static chunk URLs.This PR replaces the check with a more precise one that only flags
..when it appears as a complete path segment (surrounded by/or at a string boundary).The fix is intentionally structured for performance:
===is checked first as the cheapest comparison, followed by twoincludescalls that short-circuit. We considered a regex approach (/(?:^|\/)\.\.(?:\/|$)/) but benchmarking showedincludesruns 2–3x faster for typical URL lengths.All existing path traversal test cases continue to pass.