CVE-2026-25766

Echo is a Go web framework. In versions 5.0.0 through 5.0.2 on Windows, Echo’s middleware.Static using the default filesystem allows path traversal via backslashes, enabling unauthenticated remote file read outside the static root. In middleware/static.go, the requested path is unescaped and normalized with path.Clean (URL semantics). path.Clean does not treat \ as a path separator, so ..\ sequences remain in the cleaned path. The resulting path is then passed to currentFS.Open(...). When the filesystem is left at the default (nil), Echo uses defaultFS which calls os.Open (echo.go:792). On Windows, os.Open treats \ as a path separator and resolves ..\, allowing traversal outside the static root. Version 5.0.3 fixes the issue.