Echo is a Go web framework. Prior to 4.16.0 and 5.4.0, Echo's static file handlers can normalize dot segments after route matching and serve a file through a public static route even though the corresponding direct path is protected by route-level middleware. An unauthenticated attacker can read files that an application intended to protect with route-level middleware, when those files are also reachable through a static filesystem mount after path normalization. This vulnerability is the result of an incomplete fix for CVE-2026-55677. This issue is fixed in 4.16.0 and 5.4.0.

Affected: Go: github.com/labstack/echo/v5, Go: github.com/labstack/echo/v4

## Summary

Echo v5.2.0 contains a bypass of the fix for GHSA-vfp3-v2gw-7wfq. The fix rejects encoded path separators such as `%2F` and `%5C` before static file path unescaping, but two traversal forms still bypass route-level middleware protections for static files.

The primary bypass uses encoded dot-dot segments. A request such as `/public/%2E%2E/admin/secret.txt` passes the encoded-separator guard, is unescaped to `public/../admin/secret.txt`, then `path.Clean` resolves it to `admin/secret.txt`. If `/admin/*` is protected by middleware but the static filesystem is mounted at `/`, the protected file is returned through the public static route.

A second bypass exists when `UseEscapedPathForMatching=true`. In that mode, the router normalizes encoded separators before the static handler checks the wildcard. The handler receives a decoded wildcard with no `%` characters, so the encoded-separator guard does not run on the original encoded path.

## Impact

An unauthenticated attacker can read files that an application intended to protect with route-level middleware, when those files are also reachable through a static filesystem mount after path normalization.

The high-severity variant works with the default router configuration and requires only encoded dot-dot path segments. The direct protected route returns 403, while the public static route returns the protected file content.

The `UseEscapedPathForMatching=true` variant is lower severity because it requires a non-defa…

Affected: Ubuntu:20.04:LTS: golang-github-labstack-echo.v2, Ubuntu:20.04:LTS: golang-github-labstack-echo.v3, Ubuntu:22.04:LTS: golang-github-labstack-echo, Ubuntu:22.04:LTS: golang-github-labstack-echo.v2, Ubuntu:22.04:LTS: golang-github-labstack-echo.v3, Ubuntu:24.04:LTS: golang-github-labstack-echo, Ubuntu:26.10: golang-github-labstack-echo, Ubuntu:26.04:LTS: golang-github-labstack-echo

Echo is a Go web framework. Prior to 4.16.0 and 5.4.0, Echo's static file handlers can normalize dot segments after route matching and serve a file through a public static route even though the corresponding direct path is protected by route-level middleware. An unauthenticated attacker can read files that an application intended to protect with route-level middleware, when those files are also reachable through a static filesystem mount after path normalization. This vulnerability is the result of an incomplete fix for CVE-2026-55677. This issue is fixed in 4.16.0 and 5.4.0.