fix(web): normalize upload basenames across path styles

.jules/sentinel.md

@@ -1,3 +1,8 @@
+## 2026-07-25 - [Sentinel: Path Traversal/Zip Slip in Uploaded Filenames via Backslashes]
+**Vulnerability:** Path traversal (Zip Slip) vulnerability due to incomplete filename sanitization on POSIX servers (CWE-22 / CWE-29).
+**Learning:** On POSIX systems, `pathlib.Path(filename).name` does not treat backslashes (`\`) as directory separators. A client can supply a filename like `..\..\windows.ini`, bypassing the intended basename extraction and potentially allowing path traversal or overwriting files during extraction if the resulting filename is used to create an archive.
+**Prevention:** Explicitly normalize directory separators by replacing all backslashes with forward slashes (`filename.replace('\\', '/')`) before passing the string to path manipulation libraries like `pathlib.Path().name`.
+
 ## 2026-05-28 - [Sentinel Fixes: Temp Files & Injection]
 **Vulnerability:** Predictable Temp Files (CWE-377) and Insecure Default Permissions (CWE-276), plus Command Injection via FFmpeg Filtergraph (CWE-20).
 **Learning:** Python's `Path.with_name` plus a suffix string to make a temp file opens a race condition because it's predictable and the permissions default to system `umask` which might expose secret `0600` data. Additionally, interpolating variables directly into FFmpeg filtergraph strings allows arbitrary filter injection.

CHANGELOG.md

@@ -11,3 +11,4 @@
 
 ### Fixed
 - 단일·일괄 대상 크기 입력을 비웠을 때 이전 custom validity와 `aria-invalid` 상태를 즉시 초기화해 현재 필수 입력 상태를 정확히 전달합니다.
+- [보안] 업로드된 파일명 내 백슬래시(`\`)가 디렉토리 구분자로 처리되지 않아 발생할 수 있는 경로 탐색 및 Zip Slip 취약점(CWE-22)을 수정했습니다.

saas_web.py

@@ -486,7 +486,7 @@ def _persist_upload(file: UploadFile) -> tuple[Path, Path, Path, Path]:
         input_dir.mkdir()
         output_dir.mkdir()
 
-        safe_filename = Path(file.filename).name
+        safe_filename = Path((file.filename or "").replace("\\", "/")).name
         if not safe_filename or safe_filename in (".", ".."):
             safe_filename = "upload.tmp"
 
@@ -619,7 +619,7 @@ def shrink_media_batch(
     try:
         with zipfile.ZipFile(zip_path, "w", compression=zipfile.ZIP_STORED) as archive:
             for index, upload in enumerate(files):
-                safe_filename = Path(upload.filename or "").name
+                safe_filename = Path((upload.filename or "").replace("\\", "/")).name
                 if not safe_filename or safe_filename in (".", ".."):
                     safe_filename = "upload.tmp"
                 entry = {

tests/test_saas_web.py

@@ -560,6 +560,29 @@ def test_shrink_batch_handles_archive_failure(self, _mock_zipfile):
         self.assertEqual(response.status_code, 500)
         self.assertEqual(response.json(), {"error": "Upload processing failed"})
 
+    @patch("saas_web.media_shrinker.convert_file")
+    def test_shrink_batch_uses_safe_fallback_filename_with_backslashes(self, mock_convert_file):
+        mock_convert_file.return_value = []
+
+        response = saas_web.shrink_media_batch(
+            BackgroundTasks(),
+            files=[
+                SimpleNamespace(
+                    filename="..\\..\\windows.ini",
+                    content_type="audio/wav",
+                    file=io.BytesIO(b"dummy"),
+                )
+            ],
+            target_bytes=10000,
+        )
+
+        archive = zipfile.ZipFile(response.path)
+        manifest = json.loads(archive.read("results.json"))
+        self.assertEqual(manifest["results"][0]["filename"], "windows.ini")
+        self.assertEqual(
+            mock_convert_file.call_args.kwargs["source"].name, "windows.ini"
+        )
+
     @patch("saas_web.media_shrinker.convert_file")
     def test_shrink_batch_uses_safe_fallback_filename(self, mock_convert_file):
         mock_convert_file.return_value = []