What causes "file path %q is outside destination directory %q" in apache/beam?

Do not extract this jar — treat it as unsafe and delete it.

file path is outside destination directory

Error message

file path %q is outside destination directory %q

What it means

validatePath defends against Zip Slip: before extracting an entry it joins dest with the entry's filename and verifies via filepath.Rel that the cleaned path stays inside the destination directory. If the archive entry contains ../ segments or an absolute path escaping dest, extraction is refused with this error. This prevents a malicious jar from writing files outside the extraction directory.

Solutions

Do not extract this jar — treat it as unsafe and delete it.
Re-download the jar from the official Maven/Beam repository to replace a possibly tampered file.
Inspect the zip entries (unzip -l) to find which entry escapes the destination.
If you control jar creation, rebuild it with relative, sanitized entry names.

Defensive patterns

Strategy: validation

Validate before calling

// Pre-scan the jar for entries that would escape the destination
r, err := zip.OpenReader(jarPath)
if err != nil { return err }
for _, f := range r.File {
    p := filepath.Clean(filepath.Join(dest, f.Name))
    if !strings.HasPrefix(p, filepath.Clean(dest)+string(filepath.Separator)) {
        return fmt.Errorf("unsafe entry %q; refusing to use jar", f.Name)
    }
}

Try / catch

err := expansionx.MakeJar(ctx, url, dest)
if err != nil && strings.Contains(err.Error(), "outside destination directory") {
    os.Remove(jarPath)
    return fmt.Errorf("rejected jar from %s: path traversal detected", url)
}

Prevention

Only download jars from trusted repositories (Maven Central / official Beam artifacts).
Verify jar checksums/signatures before extraction.
Scan downloaded archives for ../ entry names in supply-chain checks.
Never extract untrusted archives into shared or home directories.

When it happens

Trigger: extractJar iterates zip entries and calls validatePath(dest, file.Name) for an entry whose cleaned path resolves outside dest (e.g. name "../../.bashrc" or "/etc/passwd").

Common situations: Extracting a tampered or maliciously crafted expansion-service jar; jars built with entries containing backslashes/absolute paths from non-standard zip tools.

Understand the failure class

Background: Path traversal blocked: "path escapes the workspace" and "outside site root" errors when a path will not stay inside its allowed directory — this error's family across 26 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/f527265daaf9867a. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/runtime/xlangx/expansionx/download.go:149

		return "", fmt.Errorf("error in creating jar %s: %w", jarPath, err)
	}

	_, err = io.Copy(file, resp.Body)
	if err != nil {
		return "", fmt.Errorf("error in coping file %s inside jar %s: %w", file.Name(), jarPath, err)
	}

	return jarPath, nil
}

func validatePath(dest, filename string) (string, error) {
	destPath := filepath.Join(dest, filename)
	cleanDest := filepath.Clean(dest)
	cleanPath := filepath.Clean(destPath)

	rel, err := filepath.Rel(cleanDest, cleanPath)
	if err != nil || strings.HasPrefix(rel, ".."+string(filepath.Separator)) || rel == ".." {
		return "", fmt.Errorf("file path %q is outside destination directory %q", filename, dest)
	}
	return cleanPath, nil
}

func extractJar(source, dest string) error {
	reader, err := zip.OpenReader(source)
	if err != nil {
		return fmt.Errorf("error opening jar for extractJar(%s,%s): %w", source, dest, err)
	}

	if err := os.MkdirAll(dest, 0700); err != nil {
		return fmt.Errorf("error creating directory %s in extractJar(%s,%s): %w", dest, source, dest, err)
	}

	for _, file := range reader.File {
		fileName, err := validatePath(dest, file.Name)
		if err != nil {
			return fmt.Errorf("error validating file path (%s, %s): %w", dest, file.Name, err)

View on GitHub (pinned to 12126d8942)