vLLM vulnerable to DoS with incorrect shape of multimodal embedding inputs

@@ -359,13 +359,19 @@ Full example: [examples/offline_inference/audio_language.py](../../examples/offl
 To input pre-computed embeddings belonging to a data type (i.e. image, video, or audio) directly to the language model,
 pass a tensor of shape `(num_items, feature_size, hidden_size of LM)` to the corresponding field of the multi-modal dictionary.
 
+You must enable this feature via `enable_mm_embeds=True`.
+
+!!! warning
+    The vLLM engine may crash if incorrect shape of embeddings is passed.
+    Only enable this flag for trusted users!
+
 ??? code
 
     ```python
     from vllm import LLM
 
     # Inference with image embeddings as input
-    llm = LLM(model="llava-hf/llava-1.5-7b-hf")
+    llm = LLM(model="llava-hf/llava-1.5-7b-hf", enable_mm_embeds=True)
 
     # Refer to the HuggingFace repo for the correct format to use
     prompt = "USER: <image>\nWhat is the content of this image?\nASSISTANT:"
@@ -397,7 +403,11 @@ For Qwen2-VL and MiniCPM-V, we accept additional parameters alongside the embedd
     image_embeds = torch.load(...)
 
     # Qwen2-VL
-    llm = LLM("Qwen/Qwen2-VL-2B-Instruct", limit_mm_per_prompt={"image": 4})
+    llm = LLM(
+        "Qwen/Qwen2-VL-2B-Instruct",
+        limit_mm_per_prompt={"image": 4},
+        enable_mm_embeds=True,
+    )
     mm_data = {
         "image": {
             "image_embeds": image_embeds,
@@ -407,7 +417,12 @@ For Qwen2-VL and MiniCPM-V, we accept additional parameters alongside the embedd
     }
 
     # MiniCPM-V
-    llm = LLM("openbmb/MiniCPM-V-2_6", trust_remote_code=True, limit_mm_per_prompt={"image": 4})
+    llm = LLM(
+        "openbmb/MiniCPM-V-2_6",
+        trust_remote_code=True,
+        limit_mm_per_prompt={"image": 4},
+        enable_mm_embeds=True,
+    )
     mm_data = {
         "image": {
             "image_embeds": image_embeds,
@@ -732,7 +747,13 @@ Full example: [examples/online_serving/openai_chat_completion_client_for_multimo
 ### Embedding Inputs
 
 To input pre-computed embeddings belonging to a data type (i.e. image, video, or audio) directly to the language model,
-pass a tensor of shape to the corresponding field of the multi-modal dictionary.
+pass a tensor of shape `(num_items, feature_size, hidden_size of LM)` to the corresponding field of the multi-modal dictionary.
+
+You must enable this feature via the `--enable-mm-embeds` flag in `vllm serve`.
+
+!!! warning
+    The vLLM engine may crash if incorrect shape of embeddings is passed.
+    Only enable this flag for trusted users!
 
 #### Image Embedding Inputs
 

@@ -20,12 +20,16 @@ You can pass prompt embeddings from Hugging Face Transformers models to the  `'p
 
 ## Online Serving
 
-Our OpenAI-compatible server accepts prompt embeddings inputs via the [Completions API](https://platform.openai.com/docs/api-reference/completions). Prompt embeddings inputs are added via a new `'prompt_embeds'` key in the JSON package.
+Our OpenAI-compatible server accepts prompt embeddings inputs via the [Completions API](https://platform.openai.com/docs/api-reference/completions). Prompt embeddings inputs are added via a new `'prompt_embeds'` key in the JSON package and are enabled by the `--enable-prompt-embeds` flag in `vllm serve`.
 
 When a mixture of `'prompt_embeds'` and `'prompt'` inputs are provided in a single request, the prompt embeds are always returned first.
 
 Prompt embeddings are passed in as base64 encoded torch tensors.
 
+!!! warning
+    The vLLM engine may crash if incorrect shape of embeddings is passed.
+    Only enable this flag for trusted users!
+
 ### Transformers Inputs via OpenAI Client
 
 First, launch the OpenAI-compatible server:

@@ -38,6 +38,7 @@ def main():
         max_num_seqs=32,
         io_processor_plugin="prithvi_to_tiff",
         model_impl="terratorch",
+        enable_mm_embeds=True,
     )
 
     pooling_params = PoolingParams(task="token_classify", activation=False)

@@ -49,6 +49,7 @@ def __init__(self, model):
             dtype="float16",
             enforce_eager=True,
             model_impl="terratorch",
+            enable_mm_embeds=True,
         )
 
     def run(self, input_data, location_coords):

@@ -19,6 +19,7 @@
 #   --task embed --trust-remote-code
 #   --skip-tokenizer-init --enforce-eager
 #   --io-processor-plugin prithvi_to_tiff
+#   --enable-mm-embeds
 
 
 def main():

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 import pytest
+import torch
 
 from vllm import LLM
 
@@ -12,8 +13,22 @@ def test_empty_prompt():
         llm.generate([""])
 
 
-@pytest.mark.skip_v1
 def test_out_of_vocab_token():
     llm = LLM(model="openai-community/gpt2", enforce_eager=True)
     with pytest.raises(ValueError, match="out of vocabulary"):
         llm.generate({"prompt_token_ids": [999999]})
+
+
+def test_require_mm_embeds():
+    llm = LLM(
+        model="llava-hf/llava-1.5-7b-hf",
+        enforce_eager=True,
+        enable_mm_embeds=False,
+    )
+    with pytest.raises(ValueError, match="--enable-mm-embeds"):
+        llm.generate(
+            {
+                "prompt": "<image>",
+                "multi_modal_data": {"image": torch.empty(1, 1, 1)},
+            }
+        )

@@ -292,3 +292,16 @@ async def test_prompt_logprobs_raises_error(
             temperature=0.0,
             extra_body={"prompt_embeds": encoded_embeds, "prompt_logprobs": True},
         )
+
+
+@pytest.mark.asyncio
+async def test_empty_prompt_embeds(
+    client_with_prompt_embeds: openai.AsyncOpenAI,
+) -> None:
+    await client_with_prompt_embeds.completions.create(
+        model=MODEL_NAME,
+        prompt="Hello",
+        max_tokens=5,
+        temperature=0.0,
+        extra_body={"prompt_embeds": []},
+    )

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 import io
+from unittest.mock import Mock
 
 # imports for structured outputs tests
 import openai
@@ -10,7 +11,8 @@
 import regex as re
 import torch
 
-from vllm.entrypoints.renderer import BaseRenderer
+from vllm.config import ModelConfig
+from vllm.entrypoints.renderer import CompletionRenderer
 
 from ...utils import RemoteOpenAIServer
 
@@ -59,6 +61,10 @@ async def test_out_of_vocab_token_ids():
 def test_load_prompt_embeds(
     dtype: torch.dtype, layout: torch.layout, seq_len: int, hidden_size: int
 ):
+    model_config = Mock(spec=ModelConfig)
+    model_config.enable_prompt_embeds = True
+    renderer = CompletionRenderer(model_config, tokenizer=None)
+
     # construct arbitrary tensors of various dtypes, layouts, and sizes.
     # We need to check against different layouts to make sure that if a user
     # uses sparse tensors to reduce the transmission size of prompt embeddings,
@@ -83,11 +89,30 @@ def test_load_prompt_embeds(
     buffer.seek(0)
     encoded_tensor = pybase64.b64encode(buffer.getvalue())
 
-    loaded_prompt_embeds = BaseRenderer.load_prompt_embeds(encoded_tensor)
+    loaded_prompt_embeds = renderer.load_prompt_embeds(encoded_tensor)
     assert len(loaded_prompt_embeds) == 1
     loaded_tensor = loaded_prompt_embeds[0]["prompt_embeds"]
     assert loaded_tensor.device.type == "cpu"
     assert loaded_tensor.layout == torch.strided
     torch.testing.assert_close(
         loaded_tensor, tensor.to("cpu").to_dense(), equal_nan=True
     )
+
+
+@pytest.mark.parametrize("dtype", [torch.float32])
+@pytest.mark.parametrize("seq_len", [2])
+@pytest.mark.parametrize("hidden_size", [2])
+def test_disable_prompt_embeds(dtype: torch.dtype, seq_len: int, hidden_size: int):
+    model_config = Mock(spec=ModelConfig)
+    model_config.enable_prompt_embeds = False
+    renderer = CompletionRenderer(model_config, tokenizer=None)
+
+    tensor = torch.randn((seq_len, hidden_size), dtype=dtype)
+
+    buffer = io.BytesIO()
+    torch.save(tensor, buffer)
+    buffer.seek(0)
+    encoded_tensor = pybase64.b64encode(buffer.getvalue())
+
+    with pytest.raises(ValueError, match="--enable-prompt-embeds"):
+        renderer.load_prompt_embeds(encoded_tensor)

@@ -15,30 +15,7 @@
 DTYPE = "float16"
 
 
-@pytest.fixture(scope="module")
-def server():
-    args = [
-        "--runner",
-        "pooling",
-        # use half precision for speed and memory savings in CI environment
-        "--dtype",
-        DTYPE,
-        "--enforce-eager",
-        "--trust-remote-code",
-        "--skip-tokenizer-init",
-        "--max-num-seqs",
-        "32",
-        "--model-impl",
-        "terratorch",
-    ]
-
-    with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:
-        yield remote_server
-
-
-@pytest.mark.asyncio
-@pytest.mark.parametrize("model_name", [MODEL_NAME])
-async def test_single_request(server: RemoteOpenAIServer, model_name: str):
+def _terratorch_dummy_inputs(model_name: str):
     pixel_values = torch.full((6, 512, 512), 1.0, dtype=torch.float16)
     location_coords = torch.full((1, 2), 1.0, dtype=torch.float16)
 
@@ -54,7 +31,7 @@ async def test_single_request(server: RemoteOpenAIServer, model_name: str):
     binary_data = buffer_coord.read()
     base64_coord_embedding = base64.b64encode(binary_data).decode("utf-8")
 
-    prompt = {
+    return {
         "model": model_name,
         "additional_data": {"prompt_token_ids": [1]},
         "encoding_format": "base64",
@@ -74,12 +51,33 @@ async def test_single_request(server: RemoteOpenAIServer, model_name: str):
         ],
     }
 
-    # test single pooling
-    response = requests.post(server.url_for("pooling"), json=prompt)
-    response.raise_for_status()
 
-    output = response.json()["data"][0]["data"]
+@pytest.mark.parametrize("model_name", [MODEL_NAME])
+async def test_single_request(model_name: str):
+    args = [
+        "--runner",
+        "pooling",
+        # use half precision for speed and memory savings in CI environment
+        "--dtype",
+        DTYPE,
+        "--enforce-eager",
+        "--trust-remote-code",
+        "--max-num-seqs",
+        "32",
+        "--model-impl",
+        "terratorch",
+        "--skip-tokenizer-init",
+        "--enable-mm-embeds",
+    ]
+
+    with RemoteOpenAIServer(MODEL_NAME, args) as server:
+        prompt = _terratorch_dummy_inputs(model_name)
+
+        # test single pooling
+        response = requests.post(server.url_for("pooling"), json=prompt)
+        response.raise_for_status()
 
-    np_response = np.frombuffer(base64.b64decode(output), dtype=np.float32)
+        output = response.json()["data"][0]["data"]
 
-    assert len(np_response) == 524288
+        np_response = np.frombuffer(base64.b64decode(output), dtype=np.float32)
+        assert len(np_response) == 524288

@@ -73,6 +73,19 @@ def phi3v_model_config_mm_interleaved():
     )
 
 
+@pytest.fixture(scope="function")
+def phi3v_model_config_image_embeds():
+    return ModelConfig(
+        PHI3V_MODEL_ID,
+        runner="generate",
+        trust_remote_code=True,
+        limit_mm_per_prompt={
+            "image": 2,
+        },
+        enable_mm_embeds=True,
+    )
+
+
 @pytest.fixture(scope="module")
 def phi3v_tokenizer():
     return get_tokenizer(PHI3V_MODEL_ID)
@@ -799,7 +812,7 @@ def test_parse_chat_messages_empty_pil_image_with_uuid(
 
 
 def test_parse_chat_messages_empty_image_embeds_with_uuid(
-    phi3v_model_config,
+    phi3v_model_config_image_embeds,
     phi3v_tokenizer,
 ):
     uuid = "abcd"
@@ -813,7 +826,7 @@ def test_parse_chat_messages_empty_image_embeds_with_uuid(
                 ],
             }
         ],
-        phi3v_model_config,
+        phi3v_model_config_image_embeds,
         phi3v_tokenizer,
         content_format="string",
     )
@@ -832,7 +845,7 @@ def test_parse_chat_messages_empty_image_embeds_with_uuid(
 
 @pytest.mark.asyncio
 async def test_parse_chat_messages_empty_image_embeds_with_uuid_async(
-    phi3v_model_config,
+    phi3v_model_config_image_embeds,
     phi3v_tokenizer,
 ):
     uuid = "abcd"
@@ -846,7 +859,7 @@ async def test_parse_chat_messages_empty_image_embeds_with_uuid_async(
                 ],
             }
         ],
-        phi3v_model_config,
+        phi3v_model_config_image_embeds,
         phi3v_tokenizer,
         content_format="string",
     )

@@ -17,6 +17,7 @@
 class MockModelConfig:
     max_model_len: int = 100
     encoder_config: dict | None = None
+    enable_prompt_embeds: bool = True
 
 
 class MockTokenizerResult:

@@ -109,8 +109,7 @@
                 limit_mm_per_prompt={"image": 4},
             )
         ],
-        # TODO: Revert to "auto" when CPU backend can use torch > 2.6
-        dtype="bfloat16" if current_platform.is_cpu() else "auto",
+        vllm_runner_kwargs={"enable_mm_embeds": True},
         marks=[pytest.mark.core_model, pytest.mark.cpu_model],
     ),
     "qwen2_5_vl": VLMTestInfo(

@@ -292,6 +292,7 @@ def run_embedding_input_test(
         tensor_parallel_size=tensor_parallel_size,
         distributed_executor_backend=distributed_executor_backend,
         default_torch_num_threads=1,
+        enable_mm_embeds=True,
     ) as vllm_model:
         outputs_per_case_for_original_input = [
             vllm_model.generate_greedy_logprobs(

@@ -34,6 +34,7 @@ def _run_test(
         dtype="half",
         enforce_eager=True,
         skip_tokenizer_init=True,
+        enable_mm_embeds=True,
         # Limit the maximum number of sequences to avoid the
         # test going OOM during the warmup run
         max_num_seqs=32,

@@ -104,6 +104,11 @@ def _initialize_kv_caches_v1(self, vllm_config):
             m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN")
         if model_arch == "WhisperForConditionalGeneration":
             m.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
+
+        extra_args = {}
+        if model_arch in ("PrithviGeoSpatialMAE", "Terratorch"):
+            extra_args["enable_mm_embeds"] = True
+
         LLM(
             model_info.default,
             tokenizer=model_info.tokenizer,
@@ -128,6 +133,7 @@ def _initialize_kv_caches_v1(self, vllm_config):
             else "vllm",
             hf_overrides=hf_overrides_fn,
             max_num_seqs=model_info.max_num_seqs,
+            **extra_args,
         )
 
 

@@ -32,6 +32,7 @@ def test_inference(
         dtype="half",
         enforce_eager=True,
         skip_tokenizer_init=True,
+        enable_mm_embeds=True,
         # Limit the maximum number of sequences to avoid the
         # test going OOM during the warmup run
         max_num_seqs=32,

@@ -38,6 +38,7 @@ def server():
         "prithvi_to_tiff",
         "--model-impl",
         "terratorch",
+        "--enable-mm-embeds",
     ]
 
     with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:

@@ -6,7 +6,6 @@
 import pytest
 import pytest_asyncio
 import regex as re
-import requests
 from openai import BadRequestError
 
 from tests.utils import RemoteOpenAIServer
@@ -686,17 +685,3 @@ async def test_invalid_grammar(client: openai.AsyncOpenAI, model_name: str):
                 "structured_outputs": {"grammar": invalid_simplified_sql_grammar}
             },
         )
-
-
-@pytest.mark.asyncio
-async def test_completion_with_empty_prompt_embeds(client: openai.AsyncOpenAI) -> None:
-    """Test completion with empty prompt embeds."""
-    payload: dict[str, object] = {"prompt": "Hello", "prompt_embeds": []}
-    headers: dict[str, str] = {"Content-Type": "application/json"}
-    # base_url = http://localhost:8000/v1/completions
-    response = requests.post(
-        f"{client.base_url}completions", headers=headers, json=payload
-    )
-    assert response.status_code == 200, (
-        f"Expected status code 200, got {response.status_code}. "
-    )

@@ -32,6 +32,7 @@ def default_image_embeds_server_args() -> list[str]:
         "--enforce-eager",
         "--limit-mm-per-prompt",
         json.dumps({"image": MAXIMUM_IMAGES}),
+        "--enable-mm-embeds",
     ]
 
 

@@ -232,8 +232,10 @@ class ModelConfig:
     output will contain token ids."""
     enable_prompt_embeds: bool = False
     """If `True`, enables passing text embeddings as inputs via the
-    `prompt_embeds` key. Note that enabling this will double the time required
-    for graph compilation."""
+    `prompt_embeds` key.
+
+    WARNING: The vLLM engine may crash if incorrect shape of embeddings is passed.
+    Only enable this flag for trusted users!"""
     served_model_name: str | list[str] | None = None
     """The model name(s) used in the API. If multiple names are provided, the
     server will respond to any of the provided names. The model name in the
@@ -303,6 +305,7 @@ class ModelConfig:
     """Configuration for multimodal model. If `None`, this will be inferred
     from the architecture of `self.model`."""
     limit_mm_per_prompt: InitVar[dict[str, int | dict[str, int]] | None] = None
+    enable_mm_embeds: InitVar[bool | None] = None
     media_io_kwargs: InitVar[dict[str, dict[str, Any]] | None] = None
     mm_processor_kwargs: InitVar[dict[str, Any] | None] = None
     mm_processor_cache_gb: InitVar[float | None] = None
@@ -421,6 +424,7 @@ def __post_init__(
         self,
         # Multimodal config init vars
         limit_mm_per_prompt: dict[str, int] | None,
+        enable_mm_embeds: bool | None,
         media_io_kwargs: dict[str, dict[str, Any]] | None,
         mm_processor_kwargs: dict[str, Any] | None,
         mm_processor_cache_gb: float | None,
@@ -731,6 +735,7 @@ def _task_to_convert(task: TaskOption) -> ConvertType:
 
             mm_config_kwargs = dict(
                 limit_per_prompt=limit_mm_per_prompt,
+                enable_mm_embeds=enable_mm_embeds,
                 media_io_kwargs=media_io_kwargs,
                 mm_processor_kwargs=mm_processor_kwargs,
                 mm_processor_cache_gb=mm_processor_cache_gb,

@@ -75,6 +75,14 @@ class MultiModalConfig:
         {"image": 16, "video": {"count": 1, "num_frames": 32, "width": 512, 
         "height": 512}}
     """
+    enable_mm_embeds: bool = False
+    """If `True`, enables passing multimodal embeddings:
+    for `LLM` class, this refers to tensor inputs under `multi_modal_data`;
+    for the OpenAI-compatible server, this refers to chat messages with content
+    `"type": "*_embeds"`.
+
+    WARNING: The vLLM engine may crash if incorrect shape of embeddings is passed.
+    Only enable this flag for trusted users!"""
     media_io_kwargs: dict[str, dict[str, Any]] = Field(default_factory=dict)
     """Additional args passed to process media inputs, keyed by modalities.
     For example, to set num_frames for video, set

@@ -438,6 +438,7 @@ class EngineArgs:
     limit_mm_per_prompt: dict[str, int | dict[str, int]] = get_field(
         MultiModalConfig, "limit_per_prompt"
     )
+    enable_mm_embeds: bool = MultiModalConfig.enable_mm_embeds
     interleave_mm_strings: bool = MultiModalConfig.interleave_mm_strings
     media_io_kwargs: dict[str, dict[str, Any]] = get_field(
         MultiModalConfig, "media_io_kwargs"
@@ -896,6 +897,9 @@ def add_cli_args(parser: FlexibleArgumentParser) -> FlexibleArgumentParser:
         multimodal_group.add_argument(
             "--limit-mm-per-prompt", **multimodal_kwargs["limit_per_prompt"]
         )
+        multimodal_group.add_argument(
+            "--enable-mm-embeds", **multimodal_kwargs["enable_mm_embeds"]
+        )
         multimodal_group.add_argument(
             "--media-io-kwargs", **multimodal_kwargs["media_io_kwargs"]
         )
@@ -1159,6 +1163,7 @@ def create_model_config(self) -> ModelConfig:
             enable_prompt_embeds=self.enable_prompt_embeds,
             served_model_name=self.served_model_name,
             limit_mm_per_prompt=self.limit_mm_per_prompt,
+            enable_mm_embeds=self.enable_mm_embeds,
             interleave_mm_strings=self.interleave_mm_strings,
             media_io_kwargs=self.media_io_kwargs,
             skip_mm_profiling=self.skip_mm_profiling,

@@ -811,6 +811,10 @@ def __init__(self, tracker: MultiModalItemTracker) -> None:
             allowed_media_domains=tracker.allowed_media_domains,
         )
 
+    @property
+    def model_config(self) -> ModelConfig:
+        return self._tracker.model_config
+
     def parse_image(self, image_url: str | None, uuid: str | None = None) -> None:
         image = self._connector.fetch_image(image_url) if image_url else None
 
@@ -822,6 +826,12 @@ def parse_image_embeds(
         image_embeds: str | dict[str, str] | None,
         uuid: str | None = None,
     ) -> None:
+        mm_config = self.model_config.get_multimodal_config()
+        if not mm_config.enable_mm_embeds:
+            raise ValueError(
+                "You must set `--enable-mm-embeds` to input `image_embeds`"
+            )
+
         if isinstance(image_embeds, dict):
             embeds = {
                 k: self._connector.fetch_image_embedding(v)
@@ -886,6 +896,10 @@ def __init__(self, tracker: AsyncMultiModalItemTracker) -> None:
             allowed_media_domains=tracker.allowed_media_domains,
         )
 
+    @property
+    def model_config(self) -> ModelConfig:
+        return self._tracker.model_config
+
     def parse_image(self, image_url: str | None, uuid: str | None = None) -> None:
         image_coro = self._connector.fetch_image_async(image_url) if image_url else None
 
@@ -897,6 +911,12 @@ def parse_image_embeds(
         image_embeds: str | dict[str, str] | None,
         uuid: str | None = None,
     ) -> None:
+        mm_config = self.model_config.get_multimodal_config()
+        if not mm_config.enable_mm_embeds:
+            raise ValueError(
+                "You must set `--enable-mm-embeds` to input `image_embeds`"
+            )
+
         future: asyncio.Future[str | dict[str, str] | None] = asyncio.Future()
 
         if isinstance(image_embeds, dict):

@@ -156,14 +156,17 @@ async def render_prompt_and_embeds(
         """
         raise NotImplementedError
 
-    @classmethod
     def load_prompt_embeds(
-        cls,
+        self,
         prompt_embeds: bytes | list[bytes],
         truncate_prompt_tokens: Annotated[int, Field(ge=0)] | None = None,
         cache_salt: str | None = None,
     ) -> list[EngineEmbedsPrompt]:
         """Load and validate base64-encoded embeddings into prompt objects."""
+        if not self.model_config.enable_prompt_embeds:
+            raise ValueError(
+                "You must set `--enable-prompt-embeds` to input `prompt_embeds`."
+            )
 
         def _load_and_validate_embed(embed: bytes) -> EngineEmbedsPrompt:
             tensor = torch.load(

@@ -1308,6 +1308,16 @@ def _to_mm_items(
         [`_get_hf_mm_data`][vllm.multimodal.processing.BaseMultiModalProcessor._get_hf_mm_data].
         """
         mm_items = self.data_parser.parse_mm_data(mm_data)
+
+        mm_config = self.info.ctx.model_config.get_multimodal_config()
+        if not mm_config.enable_mm_embeds:
+            for modality, items in mm_items.items():
+                if isinstance(items, (EmbeddingItems, DictEmbeddingItems)):
+                    raise ValueError(
+                        f"You must set `--enable-mm-embeds` to input "
+                        f"`{modality}_embeds`"
+                    )
+
         for modality, items in mm_items.items():
             self.validate_num_items(modality, len(items))