(security) Enforce frame limit in VideoMediaIO (#38636)

Signed-off-by: jperezde <jperezde@redhat.com>

tests/multimodal/media/test_video.py

@@ -239,6 +239,17 @@ def test_video_media_io_backend_env_var_fallback(monkeypatch: pytest.MonkeyPatch
         assert metadata_missing["video_backend"] == "test_video_backend_override_2"
 
 
+def _make_jpeg_b64_frames(n: int, width: int = 8, height: int = 8) -> list[str]:
+    """Return *n* tiny base64-encoded JPEG frames."""
+    frames: list[str] = []
+    for i in range(n):
+        img = Image.new("RGB", (width, height), color=(i % 256, 0, 0))
+        buf = io.BytesIO()
+        img.save(buf, format="JPEG")
+        frames.append(pybase64.b64encode(buf.getvalue()).decode("ascii"))
+    return frames
+
+
 def test_load_base64_jpeg_returns_metadata():
     """Regression test: load_base64 with video/jpeg must return metadata.
 
@@ -248,16 +259,8 @@ def test_load_base64_jpeg_returns_metadata():
     """
 
     num_test_frames = 3
-    frame_width, frame_height = 8, 8
-
-    # Build a few tiny JPEG frames and base64-encode them
-    b64_frames = []
-    for i in range(num_test_frames):
-        img = Image.new("RGB", (frame_width, frame_height), color=(i * 80, 0, 0))
-        buf = io.BytesIO()
-        img.save(buf, format="JPEG")
-        b64_frames.append(pybase64.b64encode(buf.getvalue()).decode("ascii"))
 
+    b64_frames = _make_jpeg_b64_frames(num_test_frames)
     data = ",".join(b64_frames)
 
     imageio = ImageMediaIO()
@@ -287,3 +290,52 @@ def test_load_base64_jpeg_returns_metadata():
     # Default fps=1 → duration == num_frames
     assert metadata["fps"] == 1.0
     assert metadata["duration"] == float(num_test_frames)
+
+
+def test_load_base64_jpeg_enforces_num_frames_limit():
+    """Frames beyond num_frames must be truncated in the video/jpeg path.
+
+    Without the limit an attacker can send thousands of base64 JPEG frames
+    in a single request and exhaust server memory (OOM).
+    """
+    num_frames_limit = 4
+    sent_frames = 20
+
+    b64_frames = _make_jpeg_b64_frames(sent_frames)
+    data = ",".join(b64_frames)
+
+    imageio = ImageMediaIO()
+    videoio = VideoMediaIO(imageio, num_frames=num_frames_limit)
+    frames, metadata = videoio.load_base64("video/jpeg", data)
+
+    assert frames.shape[0] == num_frames_limit
+    assert metadata["total_num_frames"] == num_frames_limit
+    assert metadata["frames_indices"] == list(range(num_frames_limit))
+
+
+def test_load_base64_jpeg_no_limit_when_num_frames_negative():
+    """When num_frames is -1, all frames should be loaded without truncation."""
+    sent_frames = 10
+
+    b64_frames = _make_jpeg_b64_frames(sent_frames)
+    data = ",".join(b64_frames)
+
+    imageio = ImageMediaIO()
+    videoio = VideoMediaIO(imageio, num_frames=-1)
+    frames, metadata = videoio.load_base64("video/jpeg", data)
+
+    assert frames.shape[0] == sent_frames
+    assert metadata["total_num_frames"] == sent_frames
+    assert metadata["frames_indices"] == list(range(sent_frames))
+
+
+def test_load_base64_jpeg_raises_on_zero_num_frames():
+    """num_frames=0 is invalid and should raise ValueError."""
+    b64_frames = _make_jpeg_b64_frames(3)
+    data = ",".join(b64_frames)
+
+    imageio = ImageMediaIO()
+    videoio = VideoMediaIO(imageio, num_frames=0)
+
+    with pytest.raises(ValueError, match="num_frames must be greater than 0 or -1"):
+        videoio.load_base64("video/jpeg", data)

vllm/multimodal/media/video.py

@@ -80,8 +80,15 @@ class VideoMediaIO(MediaIO[tuple[npt.NDArray, dict[str, Any]]]):
                 "image/jpeg",
             )
 
+            if self.num_frames > 0:
+                frame_parts = data.split(",", self.num_frames)[: self.num_frames]
+            elif self.num_frames == 0:
+                raise ValueError("num_frames must be greater than 0 or -1")
+            else:
+                frame_parts = data.split(",")
+
             frames = np.stack(
-                [np.asarray(load_frame(frame_data)) for frame_data in data.split(",")]
+                [np.asarray(load_frame(frame_data)) for frame_data in frame_parts]
             )
             total = int(frames.shape[0])
             fps = float(self.kwargs.get("fps", 1))