diff --git a/tests/entrypoints/openai/test_sparse_tensor_validation.py b/tests/entrypoints/openai/test_sparse_tensor_validation.py
new file mode 100644
index 0000000000000..907c82b57dead
--- /dev/null
+++ b/tests/entrypoints/openai/test_sparse_tensor_validation.py
@@ -0,0 +1,342 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Sparse tensor validation in embedding APIs.
+
+Tests verify that malicious sparse tensors are rejected before they can trigger
+out-of-bounds memory writes during to_dense() operations.
+"""
+
+import base64
+import io
+
+import pytest
+import torch
+
+from vllm.entrypoints.renderer import CompletionRenderer
+from vllm.multimodal.audio import AudioEmbeddingMediaIO
+from vllm.multimodal.image import ImageEmbeddingMediaIO
+
+
+def _encode_tensor(tensor: torch.Tensor) -> bytes:
+    """Helper to encode a tensor as base64 bytes."""
+    buffer = io.BytesIO()
+    torch.save(tensor, buffer)
+    buffer.seek(0)
+    return base64.b64encode(buffer.read())
+
+
+def _create_malicious_sparse_tensor() -> torch.Tensor:
+    """
+    Create a malicious sparse COO tensor with out-of-bounds indices.
+
+    This tensor has indices that point beyond the declared shape, which would
+    cause an out-of-bounds write when converted to dense format without
+    validation.
+    """
+    # Create a 3x3 sparse tensor but with indices pointing to (10, 10)
+    indices = torch.tensor([[10], [10]])  # Out of bounds for 3x3 shape
+    values = torch.tensor([1.0])
+    shape = (3, 3)
+
+    # Create sparse tensor (this will be invalid)
+    sparse_tensor = torch.sparse_coo_tensor(indices, values, shape, dtype=torch.float32)
+    return sparse_tensor
+
+
+def _create_valid_sparse_tensor() -> torch.Tensor:
+    """Create a valid sparse COO tensor for baseline testing."""
+    indices = torch.tensor([[0, 1, 2], [0, 1, 2]])
+    values = torch.tensor([1.0, 2.0, 3.0])
+    shape = (3, 3)
+
+    sparse_tensor = torch.sparse_coo_tensor(indices, values, shape, dtype=torch.float32)
+    return sparse_tensor
+
+
+def _create_valid_dense_tensor() -> torch.Tensor:
+    """Create a valid dense tensor for baseline testing."""
+    return torch.randn(10, 768, dtype=torch.float32)  # (seq_len, hidden_size)
+
+
+class TestPromptEmbedsValidation:
+    """Test sparse tensor validation in prompt embeddings (Completions API)."""
+
+    def test_valid_dense_tensor_accepted(self, model_config):
+        """Baseline: Valid dense tensors should work normally."""
+        renderer = CompletionRenderer(model_config)
+
+        valid_tensor = _create_valid_dense_tensor()
+        encoded = _encode_tensor(valid_tensor)
+
+        # Should not raise any exception
+        result = renderer.load_prompt_embeds(encoded)
+        assert len(result) == 1
+        assert result[0]["prompt_embeds"].shape == valid_tensor.shape
+
+    def test_valid_sparse_tensor_accepted(self):
+        """Baseline: Valid sparse tensors should load successfully."""
+        io_handler = ImageEmbeddingMediaIO()
+
+        valid_sparse = _create_valid_sparse_tensor()
+        encoded = _encode_tensor(valid_sparse)
+
+        # Should not raise any exception (sparse tensors remain sparse)
+        result = io_handler.load_base64("", encoded.decode("utf-8"))
+        assert result.shape == valid_sparse.shape
+
+    def test_malicious_sparse_tensor_rejected(self, model_config):
+        """Security: Malicious sparse tensors should be rejected."""
+        renderer = CompletionRenderer(model_config)
+
+        malicious_tensor = _create_malicious_sparse_tensor()
+        encoded = _encode_tensor(malicious_tensor)
+
+        # Should raise RuntimeError due to invalid sparse tensor
+        with pytest.raises((RuntimeError, ValueError)) as exc_info:
+            renderer.load_prompt_embeds(encoded)
+
+        # Error should indicate sparse tensor validation failure
+        error_msg = str(exc_info.value).lower()
+        assert "sparse" in error_msg or "index" in error_msg or "bounds" in error_msg
+
+    def test_extremely_large_indices_rejected(self, model_config):
+        """Security: Sparse tensors with extremely large indices should be rejected."""
+        renderer = CompletionRenderer(model_config)
+
+        # Create tensor with indices far beyond reasonable bounds
+        indices = torch.tensor([[999999], [999999]])
+        values = torch.tensor([1.0])
+        shape = (10, 10)
+
+        malicious_tensor = torch.sparse_coo_tensor(
+            indices, values, shape, dtype=torch.float32
+        )
+        encoded = _encode_tensor(malicious_tensor)
+
+        with pytest.raises((RuntimeError, ValueError)):
+            renderer.load_prompt_embeds(encoded)
+
+    def test_negative_indices_rejected(self, model_config):
+        """Security: Sparse tensors with negative indices should be rejected."""
+        renderer = CompletionRenderer(model_config)
+
+        # Create tensor with negative indices
+        indices = torch.tensor([[-1], [-1]])
+        values = torch.tensor([1.0])
+        shape = (10, 10)
+
+        malicious_tensor = torch.sparse_coo_tensor(
+            indices, values, shape, dtype=torch.float32
+        )
+        encoded = _encode_tensor(malicious_tensor)
+
+        with pytest.raises((RuntimeError, ValueError)):
+            renderer.load_prompt_embeds(encoded)
+
+
+class TestImageEmbedsValidation:
+    """Test sparse tensor validation in image embeddings (Chat API)."""
+
+    def test_valid_dense_tensor_accepted(self):
+        """Baseline: Valid dense tensors should work normally."""
+        io_handler = ImageEmbeddingMediaIO()
+
+        valid_tensor = _create_valid_dense_tensor()
+        encoded = _encode_tensor(valid_tensor)
+
+        # Should not raise any exception
+        result = io_handler.load_base64("", encoded.decode("utf-8"))
+        assert result.shape == valid_tensor.shape
+
+    def test_valid_sparse_tensor_accepted(self):
+        """Baseline: Valid sparse tensors should load successfully."""
+        io_handler = AudioEmbeddingMediaIO()
+
+        valid_sparse = _create_valid_sparse_tensor()
+        encoded = _encode_tensor(valid_sparse)
+
+        # Should not raise any exception (sparse tensors remain sparse)
+        result = io_handler.load_base64("", encoded.decode("utf-8"))
+        assert result.shape == valid_sparse.shape
+
+    def test_malicious_sparse_tensor_rejected(self):
+        """Security: Malicious sparse tensors should be rejected."""
+        io_handler = ImageEmbeddingMediaIO()
+
+        malicious_tensor = _create_malicious_sparse_tensor()
+        encoded = _encode_tensor(malicious_tensor)
+
+        # Should raise RuntimeError due to invalid sparse tensor
+        with pytest.raises((RuntimeError, ValueError)) as exc_info:
+            io_handler.load_base64("", encoded.decode("utf-8"))
+
+        error_msg = str(exc_info.value).lower()
+        assert "sparse" in error_msg or "index" in error_msg or "bounds" in error_msg
+
+    def test_load_bytes_validates(self):
+        """Security: Validation should also work for load_bytes method."""
+        io_handler = ImageEmbeddingMediaIO()
+
+        malicious_tensor = _create_malicious_sparse_tensor()
+        buffer = io.BytesIO()
+        torch.save(malicious_tensor, buffer)
+        buffer.seek(0)
+
+        with pytest.raises((RuntimeError, ValueError)):
+            io_handler.load_bytes(buffer.read())
+
+
+class TestAudioEmbedsValidation:
+    """Test sparse tensor validation in audio embeddings (Chat API)."""
+
+    def test_valid_dense_tensor_accepted(self):
+        """Baseline: Valid dense tensors should work normally."""
+        io_handler = AudioEmbeddingMediaIO()
+
+        valid_tensor = _create_valid_dense_tensor()
+        encoded = _encode_tensor(valid_tensor)
+
+        # Should not raise any exception
+        result = io_handler.load_base64("", encoded.decode("utf-8"))
+        assert result.shape == valid_tensor.shape
+
+    def test_valid_sparse_tensor_accepted(self):
+        """Baseline: Valid sparse tensors should be converted successfully."""
+        io_handler = AudioEmbeddingMediaIO()
+
+        valid_sparse = _create_valid_sparse_tensor()
+        encoded = _encode_tensor(valid_sparse)
+
+        # Should not raise any exception
+        result = io_handler.load_base64("", encoded.decode("utf-8"))
+        assert result.is_sparse is False
+
+    def test_malicious_sparse_tensor_rejected(self):
+        """Security: Malicious sparse tensors should be rejected."""
+        io_handler = AudioEmbeddingMediaIO()
+
+        malicious_tensor = _create_malicious_sparse_tensor()
+        encoded = _encode_tensor(malicious_tensor)
+
+        # Should raise RuntimeError due to invalid sparse tensor
+        with pytest.raises((RuntimeError, ValueError)) as exc_info:
+            io_handler.load_base64("", encoded.decode("utf-8"))
+
+        error_msg = str(exc_info.value).lower()
+        assert "sparse" in error_msg or "index" in error_msg or "bounds" in error_msg
+
+    def test_load_bytes_validates(self):
+        """Security: Validation should also work for load_bytes method."""
+        io_handler = AudioEmbeddingMediaIO()
+
+        malicious_tensor = _create_malicious_sparse_tensor()
+        buffer = io.BytesIO()
+        torch.save(malicious_tensor, buffer)
+        buffer.seek(0)
+
+        with pytest.raises((RuntimeError, ValueError)):
+            io_handler.load_bytes(buffer.read())
+
+
+class TestSparseTensorValidationIntegration:
+    """
+    These tests verify the complete attack chain is blocked at all entry points.
+    """
+
+    def test_attack_scenario_completions_api(self, model_config):
+        """
+        Simulate a complete attack through the Completions API.
+
+        Attack scenario:
+        1. Attacker crafts malicious sparse tensor
+        2. Encodes it as base64
+        3. Sends to /v1/completions with prompt_embeds parameter
+        4. Server should reject before memory corruption occurs
+        """
+        renderer = CompletionRenderer(model_config)
+
+        # Step 1-2: Attacker creates malicious payload
+        attack_payload = _encode_tensor(_create_malicious_sparse_tensor())
+
+        # Step 3-4: Server processes and should reject
+        with pytest.raises((RuntimeError, ValueError)):
+            renderer.load_prompt_embeds(attack_payload)
+
+    def test_attack_scenario_chat_api_image(self):
+        """
+        Simulate attack through Chat API with image_embeds.
+
+        Verifies the image embeddings path is protected.
+        """
+        io_handler = ImageEmbeddingMediaIO()
+        attack_payload = _encode_tensor(_create_malicious_sparse_tensor())
+
+        with pytest.raises((RuntimeError, ValueError)):
+            io_handler.load_base64("", attack_payload.decode("utf-8"))
+
+    def test_attack_scenario_chat_api_audio(self):
+        """
+        Simulate attack through Chat API with audio_embeds.
+
+        Verifies the audio embeddings path is protected.
+        """
+        io_handler = AudioEmbeddingMediaIO()
+        attack_payload = _encode_tensor(_create_malicious_sparse_tensor())
+
+        with pytest.raises((RuntimeError, ValueError)):
+            io_handler.load_base64("", attack_payload.decode("utf-8"))
+
+    def test_multiple_valid_embeddings_in_batch(self, model_config):
+        """
+        Regression test: Multiple valid embeddings should still work.
+
+        Ensures the fix doesn't break legitimate batch processing.
+        """
+        renderer = CompletionRenderer(model_config)
+
+        valid_tensors = [
+            _encode_tensor(_create_valid_dense_tensor()),
+            _encode_tensor(_create_valid_dense_tensor()),
+            _encode_tensor(_create_valid_dense_tensor()),
+        ]
+
+        # Should process all without error
+        result = renderer.load_prompt_embeds(valid_tensors)
+        assert len(result) == 3
+
+    def test_mixed_valid_and_malicious_rejected(self, model_config):
+        """
+        Security: Batch with one malicious tensor should be rejected.
+
+        Even if most tensors are valid, a single malicious one should
+        cause rejection of the entire batch.
+        """
+        renderer = CompletionRenderer(model_config)
+
+        mixed_batch = [
+            _encode_tensor(_create_valid_dense_tensor()),
+            _encode_tensor(_create_malicious_sparse_tensor()),  # Malicious
+            _encode_tensor(_create_valid_dense_tensor()),
+        ]
+
+        # Should fail on the malicious tensor
+        with pytest.raises((RuntimeError, ValueError)):
+            renderer.load_prompt_embeds(mixed_batch)
+
+
+# Pytest fixtures
+@pytest.fixture
+def model_config():
+    """Mock ModelConfig for testing."""
+    from vllm.config import ModelConfig
+
+    return ModelConfig(
+        model="facebook/opt-125m",
+        tokenizer="facebook/opt-125m",
+        tokenizer_mode="auto",
+        trust_remote_code=False,
+        dtype="float32",
+        seed=0,
+        enable_prompt_embeds=True,  # Required for prompt embeds tests
+    )
diff --git a/tests/multimodal/test_sparse_tensor_validation_unit.py b/tests/multimodal/test_sparse_tensor_validation_unit.py
new file mode 100644
index 0000000000000..2eec8ea8283a2
--- /dev/null
+++ b/tests/multimodal/test_sparse_tensor_validation_unit.py
@@ -0,0 +1,134 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Unit tests for sparse tensor validation.
+
+Simple, fast unit tests that can run without server fixtures.
+Run with: pytest tests/multimodal/test_sparse_tensor_validation_unit.py -v
+"""
+
+import io
+
+import pytest
+import torch
+
+
+class TestSparseTensorValidationContextManager:
+    """Test that torch.sparse.check_sparse_tensor_invariants() works as expected."""
+
+    def test_valid_sparse_tensor_passes(self):
+        """Valid sparse tensors should pass validation."""
+        indices = torch.tensor([[0, 1], [0, 1]])
+        values = torch.tensor([1.0, 2.0])
+        shape = (2, 2)
+
+        with torch.sparse.check_sparse_tensor_invariants():
+            tensor = torch.sparse_coo_tensor(indices, values, shape)
+            dense = tensor.to_dense()
+
+        assert dense.shape == shape
+
+    def test_out_of_bounds_indices_rejected(self):
+        """Sparse tensors with out-of-bounds indices should be rejected."""
+        indices = torch.tensor([[5], [5]])  # Out of bounds for 2x2
+        values = torch.tensor([1.0])
+        shape = (2, 2)
+
+        with pytest.raises(RuntimeError) as exc_info:  # noqa: SIM117
+            with torch.sparse.check_sparse_tensor_invariants():
+                tensor = torch.sparse_coo_tensor(indices, values, shape)
+                tensor.to_dense()
+
+        assert (
+            "index" in str(exc_info.value).lower()
+            or "bound" in str(exc_info.value).lower()
+        )
+
+    def test_negative_indices_rejected(self):
+        """Sparse tensors with negative indices should be rejected."""
+        indices = torch.tensor([[-1], [0]])
+        values = torch.tensor([1.0])
+        shape = (2, 2)
+
+        with pytest.raises(RuntimeError):  # noqa: SIM117
+            with torch.sparse.check_sparse_tensor_invariants():
+                tensor = torch.sparse_coo_tensor(indices, values, shape)
+                tensor.to_dense()
+
+    def test_without_context_manager_allows_invalid(self):
+        """
+        WITHOUT validation, invalid tensors may not immediately error.
+
+        This demonstrates the vulnerability: PyTorch 2.8.0+ doesn't validate
+        by default, which can lead to memory corruption.
+        """
+        indices = torch.tensor([[100], [100]])  # Way out of bounds
+        values = torch.tensor([1.0])
+        shape = (2, 2)
+
+        # Without validation context, this might create an invalid tensor
+        # (actual behavior depends on PyTorch version)
+        tensor = torch.sparse_coo_tensor(indices, values, shape)
+
+        # The tensor object is created, but it's invalid
+        assert tensor.is_sparse
+
+
+class TestTorchLoadWithValidation:
+    """Test torch.load() with sparse tensor validation."""
+
+    def test_load_valid_sparse_tensor_with_validation(self):
+        """Valid sparse tensors should load successfully with validation."""
+        # Create and save a valid sparse tensor
+        indices = torch.tensor([[0, 1], [0, 1]])
+        values = torch.tensor([1.0, 2.0])
+        tensor = torch.sparse_coo_tensor(indices, values, (2, 2))
+
+        buffer = io.BytesIO()
+        torch.save(tensor, buffer)
+        buffer.seek(0)
+
+        # Load with validation
+        with torch.sparse.check_sparse_tensor_invariants():
+            loaded = torch.load(buffer, weights_only=True)
+            dense = loaded.to_dense()
+
+        assert dense.shape == (2, 2)
+
+    def test_load_invalid_sparse_tensor_rejected(self):
+        """Invalid sparse tensors should be caught when loaded with validation."""
+        # Create an invalid sparse tensor (out of bounds)
+        indices = torch.tensor([[10], [10]])
+        values = torch.tensor([1.0])
+        tensor = torch.sparse_coo_tensor(indices, values, (2, 2))
+
+        buffer = io.BytesIO()
+        torch.save(tensor, buffer)
+        buffer.seek(0)
+
+        # Load with validation - should fail on to_dense()
+        with pytest.raises(RuntimeError):  # noqa: SIM117
+            with torch.sparse.check_sparse_tensor_invariants():
+                loaded = torch.load(buffer, weights_only=True)
+                loaded.to_dense()
+
+    def test_load_dense_tensor_unaffected(self):
+        """Dense tensors should work normally with the validation context."""
+        # Create and save a dense tensor
+        tensor = torch.randn(10, 20)
+
+        buffer = io.BytesIO()
+        torch.save(tensor, buffer)
+        buffer.seek(0)
+
+        # Load with validation (should have no effect on dense tensors)
+        with torch.sparse.check_sparse_tensor_invariants():
+            loaded = torch.load(buffer, weights_only=True)
+
+        assert loaded.shape == (10, 20)
+        assert not loaded.is_sparse
+
+
+if __name__ == "__main__":
+    # Allow running directly for quick testing
+    pytest.main([__file__, "-v", "--tb=short"])
diff --git a/vllm/entrypoints/renderer.py b/vllm/entrypoints/renderer.py
index 22f3c61ff73fa..0f89c840be80f 100644
--- a/vllm/entrypoints/renderer.py
+++ b/vllm/entrypoints/renderer.py
@@ -167,17 +167,20 @@ class BaseRenderer(ABC):
             )
 
         def _load_and_validate_embed(embed: bytes) -> EmbedsPrompt:
-            tensor = torch.load(
-                io.BytesIO(pybase64.b64decode(embed, validate=True)),
-                weights_only=True,
-                map_location=torch.device("cpu"),
-            )
-            assert isinstance(tensor, torch.Tensor) and tensor.dtype in (
-                torch.float32,
-                torch.bfloat16,
-                torch.float16,
-            )
-            tensor = tensor.to_dense()
+            # Enable sparse tensor integrity checks to prevent out-of-bounds
+            # writes from maliciously crafted tensors
+            with torch.sparse.check_sparse_tensor_invariants():
+                tensor = torch.load(
+                    io.BytesIO(pybase64.b64decode(embed, validate=True)),
+                    weights_only=True,
+                    map_location=torch.device("cpu"),
+                )
+                assert isinstance(tensor, torch.Tensor) and tensor.dtype in (
+                    torch.float32,
+                    torch.bfloat16,
+                    torch.float16,
+                )
+                tensor = tensor.to_dense()
             if tensor.dim() > 2:
                 tensor = tensor.squeeze(0)
                 assert tensor.dim() == 2
diff --git a/vllm/multimodal/audio.py b/vllm/multimodal/audio.py
index 062547401c3cf..51b8f77f29088 100644
--- a/vllm/multimodal/audio.py
+++ b/vllm/multimodal/audio.py
@@ -127,13 +127,21 @@ class AudioEmbeddingMediaIO(MediaIO[torch.Tensor]):
 
     def load_bytes(self, data: bytes) -> torch.Tensor:
         buffer = BytesIO(data)
-        return torch.load(buffer, weights_only=True)
+        # Enable sparse tensor integrity checks to prevent out-of-bounds
+        # writes from maliciously crafted tensors
+        with torch.sparse.check_sparse_tensor_invariants():
+            tensor = torch.load(buffer, weights_only=True)
+            return tensor.to_dense()
 
     def load_base64(self, media_type: str, data: str) -> torch.Tensor:
         return self.load_bytes(pybase64.b64decode(data, validate=True))
 
     def load_file(self, filepath: Path) -> torch.Tensor:
-        return torch.load(filepath, weights_only=True)
+        # Enable sparse tensor integrity checks to prevent out-of-bounds
+        # writes from maliciously crafted tensors
+        with torch.sparse.check_sparse_tensor_invariants():
+            tensor = torch.load(filepath, weights_only=True)
+            return tensor.to_dense()
 
     def encode_base64(self, media: torch.Tensor) -> str:
         return tensor2base64(media)
diff --git a/vllm/multimodal/image.py b/vllm/multimodal/image.py
index 789421e9e0c3b..1506ecb8c7aa0 100644
--- a/vllm/multimodal/image.py
+++ b/vllm/multimodal/image.py
@@ -122,13 +122,21 @@ class ImageEmbeddingMediaIO(MediaIO[torch.Tensor]):
 
     def load_bytes(self, data: bytes) -> torch.Tensor:
         buffer = BytesIO(data)
-        return torch.load(buffer, weights_only=True)
+        # Enable sparse tensor integrity checks to prevent out-of-bounds
+        # writes from maliciously crafted tensors
+        with torch.sparse.check_sparse_tensor_invariants():
+            tensor = torch.load(buffer, weights_only=True)
+            return tensor.to_dense()
 
     def load_base64(self, media_type: str, data: str) -> torch.Tensor:
         return self.load_bytes(pybase64.b64decode(data, validate=True))
 
     def load_file(self, filepath: Path) -> torch.Tensor:
-        return torch.load(filepath, weights_only=True)
+        # Enable sparse tensor integrity checks to prevent out-of-bounds
+        # writes from maliciously crafted tensors
+        with torch.sparse.check_sparse_tensor_invariants():
+            tensor = torch.load(filepath, weights_only=True)
+            return tensor.to_dense()
 
     def encode_base64(self, media: torch.Tensor) -> str:
         return pybase64.b64encode(media.numpy()).decode("utf-8")