Division by zero in TFLite's implementation of `BatchToSpaceNd`

Impact

The implementation of the BatchToSpaceNd TFLite operator is vulnerable to a division by zero error:

TF_LITE_ENSURE_EQ(context, output_batch_size % block_shape[dim], 0);
output_batch_size = output_batch_size / block_shape[dim];

An attacker can craft a model such that one dimension of the block input is 0. Hence, the corresponding value in block_shape is 0.

Patches

We have patched the issue in GitHub commit 2c74674348a4708ced58ad6eb1b23354df8ee044.

The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, as these are also affected and still in supported range.

For more information

Please consult our security guide for more information regarding the security model and how to contact us with issues and questions.

Attribution

This vulnerability has been reported by members of the Aivul Team from Qihoo 360.