fix(static): reject encoded path separators that bypass route-level middleware (v4 backport)#3011
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…iddleware Backport of the v5 fix (GHSA-vfp3-v2gw-7wfq) to the v4 line. An encoded path separator (%2F or %5C) in a static file URL could bypass route-level access control and disclose files. The router matches routes against the raw, still-encoded request path, so %2F is not a segment separator -- /admin%2Fsecret.txt never matches a protected /admin/* group and falls through to the static handler, which then unescaped %2F back to "/" and served admin/secret.txt from disk. Both static serving paths are affected and fixed: - StaticDirectoryHandler (echo_fs.go), used by Static/StaticFS, and the static middleware (middleware/static.go) now reject a wildcard containing an encoded separator (%2F/%2f or %5C/%5c) with 404 before unescaping, via a shared internal helper (internal/pathutil). - StaticDirectoryHandler resolves the file name with path.Clean instead of the OS-specific filepath.Clean, so a decoded backslash stays a literal character rather than being treated as a separator on Windows. (The middleware already used path.Clean.) Tests cover %2F, %5C, double-encoded %252F, group StaticFS, and the static middleware on a group, plus a unit test for the separator detector. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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This was referenced Jun 14, 2026
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v4 backport of #3009 (released in v5.2.0) for GHSA-vfp3-v2gw-7wfq.
Summary
An encoded path separator (
%2For%5C) in a static file URL could bypass route-level access control and disclose files. The router matches against the raw, still-encoded path, so%2Fis not a separator —/admin%2Fsecret.txtskips a protected/admin/*group, falls through to static serving, which then unescaped%2F→/and servedadmin/secret.txt.v4 is affected on both static surfaces:
echo_fs.goStaticDirectoryHandler(used byStatic/StaticFS) — vulnerable to%2Fand%5C(it used OS-specificfilepath.Clean).middleware/static.go— vulnerable to%2F(it already usedpath.Clean, so not%5C).Fix
%2F/%2for%5C/%5c) with404before unescaping, via a sharedinternal/pathutilhelper.StaticDirectoryHandlerswitched fromfilepath.Clean+ToSlashtopath.Clean(OS-independent; keeps backslash literal on Windows).Tests
%2F,%5C, double-encoded%252F, groupStaticFS, and the static middleware on a group; unit test for the detector.open redirect vulnerability,Directory redirect#01) that asserted the old%2f-unescaped redirect — they now correctly assert404+ noLocation.go test -race ./...andgo vet ./...pass.Targets the v4 branch for a v4.15.3 release; the advisory will be amended to add the
github.com/labstack/echo(v4) affected product once tagged.🤖 Generated with Claude Code