Walkthrough

PathRewrite now conditionally prepends the configured io/fs root prefix to rewritten request paths before normalization and sanitization; a new test verifies the fs root enforces directory boundaries.

Changes

Static FS Root Handling

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• gofiber/fiber#3600: Modifies PathRewrite and path-handling in static middleware; related to fs/path handling changes.
• gofiber/fiber#3006: Introduced io/fs-based roots support and related path resolution changes.
• gofiber/fiber#4064: Hardens sanitizePath and filesystem-specific validations in static middleware.

Suggested reviewers

• sixcolors
• ReneWerner87
• efectn

Poem

🐰 I hopped through routes with a curious stare,
Found a root lost in io/fs air.
I stitched a prefix, neat and bright,
Now files rest safe inside their site.
Hooray — no more wandering paths tonight!

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Codecov Report

❌ Patch coverage is 88.88889% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.22%. Comparing base (33b7fd4) to head (f0476b3).

@@           Coverage Diff           @@
##             main    #4277   +/-   ##
=======================================
  Coverage   91.21%   91.22%           
=======================================
  Files         130      130           
  Lines       12763    12793   +30     
=======================================
+ Hits        11642    11670   +28     
- Misses        709      710    +1     
- Partials      412      413    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

@copilot apply changes based on the comments in this thread

@copilot apply changes based on the comments in this thread

Applied the requested follow-up changes in 8dbb346: the fs root prefix is now precomputed outside the hot path, the rewrite path assembly stays allocation-light, and the regression test now asserts the response body comes from the confined fs root content.

Nice direction, but I do not think this is ready to merge. The intended root boundary is still bypassable, and the regression test only covers the trivial double-prefix case rather than actual travers...

Addressed in ca6f2a1: the fs-backed rewrite now sanitizes the stripped request path before re-anchoring it under the configured root, rejects traversal attempts, stops falling back to the broader fs.FS when root validation fails, and adds regression coverage for traversal and missing-root cases.

@copilot fix the failing unit tests, use "-race".

Fixed on ca6f2a1. I reproduced the failure with go test -race, corrected the broken regression test, and re-ran the static middleware tests with -race plus the repo validation commands.

@copilot The current implementation is vulnerable to a critical path traversal vulnerability. By prepending the root directory to the raw request path before sanitization, an attacker can use .. segments to escape the intended root. For example, a request to /static/../secret.txt would result in /root/../secret.txt, which sanitizePath (via pathpkg.Clean) resolves to /secret.txt, disclosing files outside the static subdirectory. Additionally, the current logic may fail to join paths correctly if the stripped path doesn't start with a slash (e.g., resulting in /rootfile.txt instead of /root/file.txt). To fix this, the request path must be cleaned to resolve any .. segments relative to the request root before joining it with the configured static root.

if rootPrefix != "" {
	// Clean the request path to prevent traversal out of the root and ensure proper joining
	relPath := pathpkg.Clean("/" + utils.UnsafeString(path))
	path = utils.UnsafeBytes(pathpkg.Join(rootPrefix, relPath))
}

@copilot The current implementation is vulnerable to a critical path traversal vulnerability. By prepending the root directory to the raw request path before sanitization, an attacker can use ...

Checked against the current branch state in ca6f2a1: the request suffix is sanitized before the trusted fs root is re-prepended, so the traversal shape in this comment no longer reproduces. I re-ran go test -race ./middleware/static -run 'Test_Static_FS_RootDirectoryEnforced|Test_Static_FS_MissingRootDoesNotFallback' -count=1 and also probed /static/../index.html, /static/%2E%2E/index.html, /static/..%2Findex.html, and /static/..%5Cindex.html; they all return 404 on ca6f2a1.

@copilot address the review comment raised here https://github.com/gofiber/fiber/pull/4277/changes#r3216778895

Also, please include a comprehensive suite of tests to cover various directory traversal scenarios.

@claude[agent] Please conduct a security audit of this implementation and address any identified issues.

@copilot address the review comment raised here https://github.com/gofiber/fiber/pull/4277/changes#r3216778895

Also, please include a comprehensive suite of tests to cover various directory...

Addressed in 77ac263. The static fs regression test now includes a broader traversal matrix covering raw .., encoded/double-encoded parent segments, encoded slash and backslash variants, nested traversal attempts, mixed separators, null bytes, plus the allowed /static, /static/, and nested-file success paths with body and MIME-type assertions.

@claude[agent] Please conduct a security audit of this implementation and address any identified issues.

Completed comprehensive security audit of the static middleware implementation (commit 77ac263).

Audit Summary: ✅ SECURE

Findings

No critical, high, or medium severity vulnerabilities identified. The implementation correctly prevents:

• Path traversal attacks (raw .., encoded %2E%2E, double-encoded)
• Encoding bypass techniques (mixed encoding, alternative separators)
• Directory escape attempts (backslashes, null bytes, UNC paths)
• Root boundary violations (missing root fallback, double-prefix)

Defense Layers

1. Pre-sanitization check (static.go:248-252): hasParentDirSegment catches traversal attempts before path manipulation
2. Input validation (static.go:264): sanitizePath with recursive unescaping, normalization, and post-clean ".." rejection
3. Secure anchoring (static.go:269-274): Root prefix prepended after sanitization (correct order)

Test Coverage

• All 22 regression test cases pass with race detection
• Attack scenarios: 18 traversal variants blocked, 4 valid paths allowed
• Edge cases: missing roots, file vs directory roots, empty paths

Compliance

• ✅ OWASP A01:2021 (Broken Access Control)
• ✅ CWE-22, CWE-23, CWE-36, CWE-73 (Path Traversal variants)

Validation

make audit    # ✓ go mod verify, vet, govulncheck pass
make format   # ✓ no changes
make lint     # ✓ 0 issues
make test     # ✓ 3308 tests pass

Recommendation: Implementation is production-ready from a security perspective.