Claude-coauthored tar extraction failed to exclude link-based targets before truncating files, allowing a crafted archive to overwrite arbitrary files.

+	for {+		header, err := tr.Next()+		if err == io.EOF {+			return nil+		}++		if err != nil {+			return fmt.Errorf("error reading tar: %w", err)+		}++		targetPath, err := validatePath(destPath, header.Name)+		if err != nil {+			return err+		}++		switch header.Typeflag {+		case tar.TypeDir:+			if err = os.MkdirAll(targetPath, os.FileMode(header.Mode)); err != nil {+				return fmt.Errorf("error creating directory %s: %w", targetPath, err)+			}++		case tar.TypeReg:+			if err = extractFile(tr, targetPath, header); err != nil {

++		default:+			// Skip unsupported entry types.+			continue+		}+	}+}++func extractFile(tr *tar.Reader, targetPath string, header *tar.Header) error {+	if err := os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {+		return fmt.Errorf("error creating parent directory for %s: %w", targetPath, err)+	}++	f, err := os.OpenFile(targetPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(header.Mode))+	if err != nil {+		return fmt.Errorf("error creating file %s: %w", targetPath, err)+	}+	defer f.Close()++	if _, err = io.Copy(f, io.LimitReader(tr, header.Size)); err != nil {+		return fmt.Errorf("error extracting file %s: %w", targetPath, err)+	}++	return nil

+	// Remove existing file/symlink at target path before creating new symlink.+	_ = os.Remove(targetPath)++	if err := os.Symlink(header.Linkname, targetPath); err != nil {+		return fmt.Errorf("error creating symlink %s: %w", targetPath, err)+	}++	return nil+}++// validatePath checks that the given tar entry name resolves to a path+// within the destination directory. Returns the cleaned absolute path.+func validatePath(basePath, entryName string) (string, error) {+	cleanBase := filepath.Clean(basePath)+	fullPath := filepath.Join(cleanBase, filepath.FromSlash(entryName))+	cleanPath := filepath.Clean(fullPath)++	// The path must be the base itself or a child of it.+	if cleanPath == cleanBase {+		return cleanPath, nil+	}++	if !strings.HasPrefix(cleanPath, cleanBase+string(filepath.Separator)) {+		return "", fmt.Errorf("path traversal detected: %s", entryName)+	}

@@ -294,8 +294,6 @@ func archivePath(tarWriter *tar.Writer, basePath string) error { 		relPath = filepath.ToSlash(relPath)  		switch {-		case info.Mode()&os.ModeSymlink != 0:-			return archiveSymlink(tarWriter, basePath, path, relPath) 		case info.IsDir(): 			return archiveDir(tarWriter, relPath, info) 		case info.Mode().IsRegular():@@ -345,39 +343,8 @@ func archiveFile(tarWriter *tar.Writer, absPath, relPath string, info os.FileInf 	return nil } -func archiveSymlink(tarWriter *tar.Writer, basePath, absPath, relPath string) error {-	linkTarget, err := os.Readlink(absPath)-	if err != nil {-		return fmt.Errorf("error reading symlink %s: %w", absPath, err)-	}--	// Validate the symlink target stays within the base path.-	if err = validateSymlink(basePath, linkTarget, absPath); err != nil {-		// Skip symlinks that escape the base directory.-		return nil-	}--	// Convert absolute targets to relative paths for archive portability.-	if filepath.IsAbs(linkTarget) {-		linkTarget, err = filepath.Rel(filepath.Dir(absPath), linkTarget)-		if err != nil {-			// Skip if we can't compute a relative path.-			return nil-		}-	}--	header := &tar.Header{-		Typeflag: tar.TypeSymlink,-		Name:     relPath,-		Linkname: filepath.ToSlash(linkTarget),-	}--	return tarWriter.WriteHeader(header)-}- // extractTar reads a tar archive and extracts its contents to destPath. // All paths are validated to prevent directory traversal attacks.-// Symlinks with targets outside destPath are rejected. // // For directories: creates destPath if needed and extracts contents. // For single files: destPath can be an existing directory (extract file there),@@ -472,11 +439,6 @@ func extractTarEntries(tarReader *tar.Reader, destPath, stripPrefix string) erro 				return err 			} -		case tar.TypeSymlink:-			if err = extractSymlink(destPath, root, relPath, header); err != nil {-				return err-			}- 		default: 			// Skip unsupported entry types. 			continue@@ -523,25 +485,6 @@ func extractSingleFile(tarReader *tar.Reader, destPath string, header *tar.Heade

-	}--	// Remove existing file/symlink at target path before creating new symlink.-	_ = root.Remove(relPath)--	// The parent components were created through the root, so they are genuine-	// directories (not attacker-planted symlinks); creating the link does not follow-	// any path component and the validated target stays within destPath.-	if err := os.Symlink(header.Linkname, targetPath); err != nil {-		return fmt.Errorf("error creating symlink %s: %w", relPath, err)-	}-