diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 858d9d42..7c13e7b9 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -1,3 +1,7 @@
+## 2026-08-03 - [Fix Path Traversal in Zip Generation]
+**Vulnerability:** Client-side Path Traversal (Zip Slip) possible on Windows due to preserving backslashes in filenames when creating ZIP archive.
+**Learning:** `Path.name` on POSIX does not treat `\` as a directory separator, meaning Windows path payloads preserve their traversal sequences in the ZIP `arcname`.
+**Prevention:** Explicitly sanitize filenames by standardizing `\` to `/` before using `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.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ebfe94a6..80ac63f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,3 +4,4 @@
 ### Added
 - 다중 파일 업로드 선택 시 즉각적인 파일 개수 피드백 및 제한 초과 경고 메시지 추가
 - 일괄 업로드 폼에 대상 바이트 프리셋 버튼과 총 파일 크기 미리보기를 추가하여 사용성을 개선했습니다.
+- **보안 수정:** ZIP 아카이브 생성 시 백슬래시(`\`)가 포함된 파일 이름으로 인해 발생할 수 있는 Windows 클라이언트 측 경로 탐색(Zip Slip) 취약점을 수정했습니다.
diff --git a/saas_web.py b/saas_web.py
index 3a7b0352..85f3dd2b 100644
--- a/saas_web.py
+++ b/saas_web.py
@@ -462,7 +462,8 @@ def _persist_upload(file: UploadFile) -> tuple[Path, Path, Path, Path]:
         input_dir.mkdir()
         output_dir.mkdir()
 
-        safe_filename = Path(file.filename).name
+        raw_name = getattr(file, "filename", "") or ""
+        safe_filename = Path(raw_name.replace("\\", "/")).name
         if not safe_filename or safe_filename in (".", ".."):
             safe_filename = "upload.tmp"
 
@@ -595,7 +596,8 @@ 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
+                raw_name = getattr(upload, "filename", "") or ""
+                safe_filename = Path(raw_name.replace("\\", "/")).name
                 if not safe_filename or safe_filename in (".", ".."):
                     safe_filename = "upload.tmp"
                 entry = {
diff --git a/tests/test_saas_web.py b/tests/test_saas_web.py
index 57b879d1..414d85ee 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -558,6 +558,29 @@ 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_sanitizes_windows_path_traversal(self, mock_convert_file):
+        def fake_convert(source, root, output_dir, target_bytes):
+            output_path = Path(output_dir) / (Path(source).stem + ".flac")
+            output_path.write_bytes(b"shrunk")
+            result = MagicMock(spec=ConversionResult)
+            result.output_path = output_path
+            return [result]
+
+        mock_convert_file.side_effect = fake_convert
+
+        response = client.post(
+            "/shrink-batch",
+            files=[
+                ("files", ("..\\..\\windows\\system32\\cmd.exe", b"audio", "audio/wav")),
+            ],
+            data={"target_bytes": 10000},
+        )
+        self.assertEqual(response.status_code, 200)
+        archive = zipfile.ZipFile(io.BytesIO(response.content))
+        names = archive.namelist()
+        self.assertIn("01_cmd.flac", names)
+
     @patch("saas_web.media_shrinker.convert_file")
     def test_shrink_batch_uses_safe_fallback_filename(self, mock_convert_file):
         mock_convert_file.return_value = []