Echo is a Go web framework. Prior to 4.15.3 and 5.2.0, middleware.Static can decode an already decoded Request.URL.Path a second time. Double-encoded separators can consequently be reconstructed before filesystem resolution. This can reach a file under a guarded route when the static middleware is registered globally. This issue is fixed in 4.15.3 and 5.2.0.

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

## Summary

Commit a9ede66a (PR #3006, issue #2599) silently fixed a path traversal vulnerability in the Echo web framework's static file middleware.

## Vulnerability

The static middleware double-unescaped URL paths. Go's net/http already decodes Request.URL.Path, but middleware/static.go unconditionally called url.PathUnescape() again:

```go // BEFORE (vulnerable) pathUnescape := true ```

This reassembled path traversal sequences from double-encoded input. An attacker could send GET /%2e%2e%2fsecret.txt or /..%252fsecret.txt and the double-unescape would produce ../secret.txt.

## Fix ```go // AFTER (fixed) pathUnescape := false ```

The commit's test TestStatic_percentEncodedTraversalIsBlocked explicitly verifies traversal vectors are blocked.

## Impact Arbitrary file read from server filesystem via percent-encoded path traversal.

## References - Fix: https://github.com/labstack/echo/commit/a9ede66a - Issue: https://github.com/labstack/echo/issues/2599 - PR: https://github.com/labstack/echo/pull/3006

## Patches

Fixed in `github.com/labstack/echo/v5` v5.2.0 and `github.com/labstack/echo/v4` v4.15.3, where the Static middleware stopped unescaping an already decoded path. Maintainer analysis: reading files outside the configured root could not be reproduced; the confirmed impact was that a double-encoded slash (`%252F`) could reach a file under a guarded route when the Static middleware is registered globally. Upgrade to v5.4.0 / v4.16.0 or later, which also includes…

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 4.15.3 and 5.2.0, middleware.Static can decode an already decoded Request.URL.Path a second time. Double-encoded separators can consequently be reconstructed before filesystem resolution. This can reach a file under a guarded route when the static middleware is registered globally. This issue is fixed in 4.15.3 and 5.2.0.