fix(clashapi): prevent zip slip in external UI download

experimental/clashapi/server_resources.go

@@ -101,6 +101,7 @@ func (s *Server) downloadZIP(body io.Reader, output string) error {
 	}
 	defer reader.Close()
 	trimDir := zipIsInSingleDirectory(reader.File)
+	cleanOutput := filepath.Clean(output) + string(os.PathSeparator)
 	for _, file := range reader.File {
 		if file.FileInfo().IsDir() {
 			continue
@@ -118,6 +119,10 @@ func (s *Server) downloadZIP(body io.Reader, output string) error {
 			return err
 		}
 		savePath := filepath.Join(saveDirectory, pathElements[len(pathElements)-1])
+		cleanSavePath := filepath.Clean(savePath)
+		if !strings.HasPrefix(cleanSavePath, cleanOutput) {
+			return os.ErrPermission
+		}
 		err = downloadZIPEntry(s.ctx, file, savePath)
 		if err != nil {
 			return err

experimental/clashapi/server_resources_test.go

@@ -0,0 +1,46 @@
+package clashapi
+
+import (
+	"archive/zip"
+	"bytes"
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestDownloadZIPZipSlip(t *testing.T) {
+	tempDir := t.TempDir()
+
+	var buf bytes.Buffer
+
+	zw := zip.NewWriter(&buf)
+
+	_, err := zw.Create("../../../pwned.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = zw.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	server := &Server{
+		ctx: context.Background(),
+	}
+
+	err = server.downloadZIP(bytes.NewReader(buf.Bytes()), tempDir)
+
+	if err == nil {
+		t.Fatal("expected zip slip error")
+	}
+
+	outsidePath := filepath.Join(tempDir, "..", "..", "..", "pwned.txt")
+
+	_, err = os.Stat(outsidePath)
+
+	if !os.IsNotExist(err) {
+		t.Fatal("zip slip created file outside target directory")
+	}
+}