Echo: Encoded slash (%2F) bypasses route-level protection and exposes static files

### Summary Echo's router and static file handler disagree on URL path decoding. The router matches routes using the raw encoded path (preserving `%2F` as-is), while `StaticDirectoryHandler` unescapes `%2F` to `/` before resolving filesystem paths. This allows an attacker to bypass route-level access controls and read static files without authorization. ### Details **Root cause 1 — `router.go` lines 798-802:** The router uses `req.URL.RawPath` for route matching when `useEscapedPathForRouting` is false (the default). This means `/admin%2Fsecret.txt` is treated as a single path segment and does NOT match the `/admin/*` route pattern. ```go if !r.useEscapedPathForRouting && req.URL.RawPath != "" { path = req.URL.RawPath } ``` **Root cause 2 — `echo.go` lines 559-568:** `StaticDirectoryHandler` calls `url.PathUnescape()` on the path parameter before opening files. This converts `%2F` back to `/`, resolving `admin/secret.txt` on disk. ```go if !disablePathUnescaping { tmpPath, err := url.PathUnescape(p) p = tmpPath } name := filepath.ToSlash(filepath.Clean(strings.TrimPrefix(p, "/"))) ``` ### PoC (Screenshot) Sample: <img width="1291" height="970" alt="image" src="https://github.com/user-attachments/assets/0bc58059-3e6d-4678-ab25-a5c79b006738" /> 403: <img width="526" height="194" alt="image" src="https://github.com/user-attachments/assets/2f55ffdd-87b2-4a1b-8a13-130ebad0f257" /> Bypass with encoded slash: <img width="592" height="203" alt="image" src="https://github.com/user-attachments/assets/1191cd39-ae8f-4d7e-8fb1-cb9cf31f484f" /> ### Impact Unauthorized static file disclosure. Applications that protect route prefixes with authentication middleware while also serving static files from a broader root are vulnerable. An attacker only needs to encode the slash (`/` → `%2F`) in the URL to bypass all route-level protection. Common affected pattern: ```go adminGroup := e.Group("/admin", authMiddleware) e.StaticFS("/", os.DirFS("public")) ```

Source published

25 Aug 2026 16:13:29 UTC

Source modified

10 Sep 2026 03:51:14 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Publisher rating · HIGH