🐛 bug: reject static partial wildcard matches that cross a path segment boundary by drakeo338 · Pull Request #4728 · gofiber/fiber

drakeo338 · 2026-09-30T17:16:22Z

Description

A static route with a partial wildcard such as /static* also matched /staticprivate/secret.txt, and the file server served <root>/private/secret.txt, skipping any middleware mounted on /static/private. The static handler now answers 404 unless the path continues at a segment boundary after the route prefix.

Changes introduced

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Type of change

New feature (non-breaking change which adds functionality)
Enhancement (improvement to existing features and functionality)
Documentation update (changes to documentation)
Performance improvement (non-breaking change which improves efficiency)
Code consistency (non-breaking change which improves code reliability and robustness)

Checklist

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Followed the inspiration of the Express.js framework for new functionalities, making them similar in usage.
Conducted a self-review of the code and provided comments for complex or critical parts.
Updated the documentation in the /docs/ directory for Fiber's documentation.
Added or updated unit tests to validate the effectiveness of the changes or new features.
Ensured that new and existing unit tests pass locally with the changes.
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Aimed for optimal performance with minimal allocations in the new code.
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…nt boundary A route such as /static* also matches /staticprivate/secret.txt, which the file server served from <root>/private/secret.txt and so skipped middleware mounted on /static/private. Answer 404 unless the path continues at a segment boundary.

coderabbitai · 2026-09-30T17:16:45Z

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Reviewing files that changed from the base of the PR and between 54f5fec and 91bcbeb.

📒 Files selected for processing (4)

docs/middleware/static.md
docs/whats_new.md
middleware/static/static.go
middleware/static/static_test.go

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Walkthrough

The static handler now rejects partial-wildcard paths that continue beyond the route prefix without a slash. Tests cover matching paths, sibling-prefix paths, and protected paths. The documentation describes this route behavior.

Changes

Static path boundary

Layer / File(s)	Summary
Partial-wildcard path validation `middleware/static/static.go`	`newFileServer` marks non-empty wildcard prefixes that do not end in `/` as requiring a segment boundary. `requestPath` returns the invalid-path sentinel when a longer request path continues without a slash.
Boundary behavior and route guidance `middleware/static/static_test.go`, `docs/middleware/static.md`, `docs/whats_new.md`	Tests cover `/static/x`, sibling-prefix paths, protected middleware, and matching routes with `+`, a parameter, or a slash before `*`. The documentation describes which paths a trailing wildcard route matches.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: 🔵 Low · up to 91bcb

A static root containing __fiber_invalid__ can return that file for a sibling-prefix request instead of 404. This is a narrow edge case, so the remaining merge risk is low.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 91bcb

The change narrows static-file access and blocks the ordinary path-prefix bypass. However, rejection still depends on a special filename being absent rather than stopping file serving directly. That weakness already existed for invalid paths; broader file access or additional privileges were not demonstrated.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

inferred — An unauthenticated requester can select boundary-failing paths on an exposed GET or HEAD static route. The demonstrated collision is limited to the fixed sentinel lookup accessible to the serving process; it does not establish arbitrary filesystem escape, cross-tenant access, or additional service privileges. Actual sensitive contents and deployment exposure are unknown.

Security Findings and Attack Paths

inferred — If an ordinary static root contains a readable fiber_invalid file, /staticx on /static* can serve that file instead of producing the intended rejection. The collision mechanism predates this PR: sanitizer failures already returned the same sentinel and reached the same serving sink. Head adds aliases to this existing exposure, rather than demonstrating a broader disclosure capability.

Trust Boundaries and Controls

observed — Middleware prefix matching accepts an exact prefix or slash boundary. Ordered dispatch and static terminal behavior mean protection must execute before successful static serving. The patch addresses the separate static-prefix interpretation mismatch but does not change this existing ordering requirement.

Hardening Proposals

proposed — Represent invalid paths as an explicit non-serving outcome and select the intended rejection or fallback before invoking the filesystem handler. Validate that outcome with a root containing fiber_invalid, so control effectiveness cannot depend on filesystem contents.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files. (2 skipped: 2…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: rejecting static partial-wildcard matches that cross path segment boundaries.
Description check	✅ Passed	The description explains the defect, references issue `#4727`, states the resulting behavior, and records the test and documentation context. Some checklist items remain unticked, but the description is…
Linked Issues check	✅ Passed	The change satisfies issue [`#4727`]. Static handling rejects a partial `*` match when the remaining path does not start with `/`. Tests cover rejected paths such as `/staticprivate/secret.txt`, accepte…
Out of Scope Changes check	✅ Passed	The changes modify static path handling, regression tests, and related documentation. Each change supports the segment-boundary fix in [`#4727`]. No unrelated change is identified.

Full details: Docstring Coverage

Explanation

Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files. (2 skipped: 2 unsupported.)

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Actionable comments posted: 1

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Inline comments:
Review comments at @middleware/static/static.go:
- Line 65: Update fileServer.requestPath to return an explicit validity result
for invalid partial-wildcard paths, and have the caller reject invalid paths
with a 404 before invoking server.handler. Add a regression test with
__fiber_invalid__ in the static root to verify that /staticx does not serve the
sentinel-named file.

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📒 Files selected for processing (2)

middleware/static/static.go
middleware/static/static_test.go

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ReneWerner87

Checked this against main. The case from #4727 is fixed: under app.Get("/static*", ...), /staticprivate/secret.txt answers 404, and segment-bounded mounts are unchanged. One point:

The check also fires on routes that are not /prefix* mounts. It applies to every route with a prefix longer than one byte, so these were served on main and now answer 404:

app.Get("/static+", static.New(dir)): /static/app.js
app.Get("/:lang/*", static.New("index.html")): /en/dashboard
app.Get("/users/:id", static.New("app.js")): /users/1234

Limiting it to prefixes that were cut at a * and do not end in / should keep the intended change and leave these alone.

Separately, /prefix* is the documented mount form (docs/middleware/static.md, whats_new.md), so a sentence there would help: under /static*, /static-v2/app.js or /staticapp.js are no longer served.

codecov · 2026-10-01T16:49:23Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.95%. Comparing base (0a8f363) to head (91bcbeb).
⚠️ Report is 33 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4728   +/-   ##
=======================================
  Coverage   94.95%   94.95%           
=======================================
  Files         141      141           
  Lines       17532    17537    +5     
=======================================
+ Hits        16648    16653    +5     
  Misses        555      555           
  Partials      329      329

Flag	Coverage Δ
unittests	`94.95% <100.00%> (+<0.01%)`	⬆️

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Apply the check only to a route cut at a * whose prefix does not end in /, so /static+, /:lang/* and /users/:id are served as before. Document the change for /static*. Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

drakeo338 · 2026-10-01T16:54:50Z

The check now only applies to a *-cut prefix not ending in /, your three routes are covered by tests and served as on main, and the docs note the change.

welcome · 2026-10-08T10:18:05Z

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ReneWerner87 · 2026-10-08T10:28:18Z

Reviewed head 91bcbeb against main.

Verified (temporary test, GET and HEAD, main vs. this PR) with app.Get("/static*", static.New(dir)):

Request	main	PR
`/static`, `/static/`, `/static/x`	200	200
`/staticx`	200	404
`/staticprivate/secret.txt`, `/STATICprivate/secret.txt` (case-insensitive routing)	200 `SECRET`	404
group `g.Get("/s*")`: `/g/sprivate/secret.txt`	200 `SECRET`	404
`/static%2Fprivate/secret.txt`, `/static//x`	404	404
`app.Use("/use", ...)`: `/use/x` / `/usex`	200 / 404	200 / 404

HEAD matches GET throughout. Other methods still go to c.Next(), as before. The 404 fits RFC 9110 §15.5.5: this route has no resource for /staticx, and NotFoundHandler still runs. The extra cost on the hot path is one bool check and one byte compare, which is negligible. Both new tests call t.Parallel(), and I found no _ discards.

Layer: I think the static handler is the right place for this fix. In the router, /prefix* matching without a segment boundary is general partial-wildcard behavior. Changing it there would affect every handler, not just static. The flaw in #4727 is that static treats the stripped remainder as a path below the mount, so the check belongs where the prefix is stripped.

One question (minor, not blocking): file roots. The check runs before the rootIsFile switch (middleware/static/static.go:65). So app.Get("/app*", static.New("index.html")) now answers 404 for /appx, while main serves index.html there. Bypass is not a concern for a file root, because the same file is served whatever the remainder is. If keeping that behavior is wanted, add !s.rootIsFile to the condition. If the change is intended, the new doc sentences already cover it in general terms. Separately, and already broken on main, so not part of this PR: a route with a parameter before the * (for example /v:ver*) strips len("/v:ver") bytes and doesn't serve.

Merge state: CI is green. All check runs on 91bcbeb passed, except the two Dependabot automerge jobs, which were skipped. blocked comes from branch protection, which requires 1 approving review from a code owner. There are no approvals yet, and the requested reviewers are gaby, sixcolors and efectn. The earlier maintainer point (the check firing on /static+, /:lang/*, /users/:id) and the docs note have been addressed.

Checks I ran on the PR head: make lint gave 0 issues. make test passed: 6468 tests, 6 skipped.

Generated by Claude Code

drakeo338 requested a review from a team as a code owner September 30, 2026 17:16

drakeo338 requested review from ReneWerner87, efectn, gaby and sixcolors September 30, 2026 17:16

ReneWerner87 added v3 ☢️ Bug labels Sep 30, 2026

ReneWerner87 added this to the v3 milestone Sep 30, 2026

ReneWerner87 added this to v3 Sep 30, 2026

coderabbitai Bot reviewed Sep 30, 2026

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Comment thread middleware/static/static.go Resolved

ReneWerner87 reviewed Oct 1, 2026

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Mucahitakin mentioned this pull request Oct 6, 2026

🐛 bug: enforce static partial wildcard segment boundaries #4742

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ReneWerner87 approved these changes Oct 8, 2026

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ReneWerner87 merged commit 410497f into gofiber:main Oct 8, 2026
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ReneWerner87 modified the milestones: v3, v3.6.0 Oct 12, 2026

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🐛 bug: reject static partial wildcard matches that cross a path segment boundary - #4728

🐛 bug: reject static partial wildcard matches that cross a path segment boundary#4728
ReneWerner87 merged 2 commits into
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drakeo338:claude/4727-fix

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