diff --git a/src/extension_shield/api/main.py b/src/extension_shield/api/main.py
index 3ebbc4c..fd344ea 100644
--- a/src/extension_shield/api/main.py
+++ b/src/extension_shield/api/main.py
@@ -3016,6 +3016,18 @@ async def generate_pdf_report(extension_id: str) -> Response:
         raise HTTPException(status_code=500, detail=f"Failed to generate PDF: {str(e)}")
 
 
+def _can_view_scan_files(request_user_id: str | None, results: dict[str, Any]) -> bool:
+    """Allow file access for public scans and the owning user for private scans."""
+    if not isinstance(results, dict):
+        return False
+    if results.get("visibility") != "private":
+        return True
+    owner_user_id = results.get("user_id")
+    if not owner_user_id or not request_user_id:
+        return False
+    return str(owner_user_id) == str(request_user_id)
+
+
 @app.get("/api/scan/files/{extension_id}")
 async def get_file_list(extension_id: str, http_request: Request) -> FileListResponse:
     """
@@ -3038,6 +3050,9 @@ async def get_file_list(extension_id: str, http_request: Request) -> FileListRes
     if not results:
         raise HTTPException(status_code=404, detail="Extension not found")
 
+    if not _can_view_scan_files(user_id, results):
+        raise HTTPException(status_code=404, detail="Scan results not found")
+
     extracted_path = results.get("extracted_path")
     if not extracted_path or not os.path.exists(extracted_path):
         raise HTTPException(status_code=404, detail="Extracted files not found")
@@ -3069,6 +3084,9 @@ async def get_file_content(extension_id: str, file_path: str, http_request: Requ
     if not results:
         raise HTTPException(status_code=404, detail="Extension not found")
 
+    if not _can_view_scan_files(user_id, results):
+        raise HTTPException(status_code=404, detail="Scan results not found")
+
     extracted_path = results.get("extracted_path")
     if not extracted_path:
         raise HTTPException(status_code=404, detail="Extracted files not found")
diff --git a/tests/api/test_private_scan_file_access.py b/tests/api/test_private_scan_file_access.py
new file mode 100644
index 0000000..594f590
--- /dev/null
+++ b/tests/api/test_private_scan_file_access.py
@@ -0,0 +1,90 @@
+"""
+Tests for scan file access control.
+
+Security regression coverage:
+- Public scans remain accessible.
+- Private scans are hidden from non-owners.
+- File list and file content endpoints do not leak private scan existence.
+"""
+
+from pathlib import Path
+import tempfile
+
+import pytest
+from fastapi.testclient import TestClient
+
+from extension_shield.api.main import app, scan_results
+
+
+@pytest.fixture
+def client() -> TestClient:
+    return TestClient(app)
+
+
+@pytest.fixture
+def extracted_dir() -> Path:
+    with tempfile.TemporaryDirectory() as temp_dir:
+        root = Path(temp_dir)
+        (root / "manifest.json").write_text('{"name":"Public Extension"}', encoding="utf-8")
+        scripts_dir = root / "scripts"
+        scripts_dir.mkdir()
+        (scripts_dir / "content.js").write_text("console.log('hello');", encoding="utf-8")
+        yield root
+
+
+class TestPrivateScanFileAccess:
+    def test_public_scan_file_list_is_accessible(self, client: TestClient, extracted_dir: Path):
+        ext_id = "abcdefghijklmnopabcdefghijklmnop"
+        scan_results[ext_id] = {
+            "extension_id": ext_id,
+            "status": "completed",
+            "visibility": "public",
+            "user_id": None,
+            "extracted_path": str(extracted_dir),
+        }
+
+        try:
+            response = client.get(f"/api/scan/files/{ext_id}")
+
+            assert response.status_code == 200
+            files = response.json()["files"]
+            assert "manifest.json" in files
+            assert "scripts/content.js" in files
+        finally:
+            scan_results.pop(ext_id, None)
+
+    def test_private_scan_file_list_hidden_from_non_owner(self, client: TestClient, extracted_dir: Path):
+        ext_id = "bcdefghijklmnopabcdefghijklmnopa"
+        scan_results[ext_id] = {
+            "extension_id": ext_id,
+            "status": "completed",
+            "visibility": "private",
+            "user_id": "owner-user-123",
+            "extracted_path": str(extracted_dir),
+        }
+
+        try:
+            response = client.get(f"/api/scan/files/{ext_id}")
+
+            assert response.status_code == 404
+            assert response.json()["detail"] == "Scan results not found"
+        finally:
+            scan_results.pop(ext_id, None)
+
+    def test_private_scan_file_content_hidden_from_non_owner(self, client: TestClient, extracted_dir: Path):
+        ext_id = "cdefghijklmnopabcdefghijklmnopab"
+        scan_results[ext_id] = {
+            "extension_id": ext_id,
+            "status": "completed",
+            "visibility": "private",
+            "user_id": "owner-user-123",
+            "extracted_path": str(extracted_dir),
+        }
+
+        try:
+            response = client.get(f"/api/scan/file/{ext_id}/scripts/content.js")
+
+            assert response.status_code == 404
+            assert response.json()["detail"] == "Scan results not found"
+        finally:
+            scan_results.pop(ext_id, None)