## TFSA-2021-090: Division by zero in TFLite's implementation of hashtable lookup

### CVE Number
CVE-2021-29604

### Impact
The TFLite implementation of hashtable lookup is [vulnerable to a division by
zero
error](https://github.com/tensorflow/tensorflow/blob/1a8e885b864c818198a5b2c0cbbeca5a1e833bc8/tensorflow/lite/kernels/hashtable_lookup.cc#L114-L115):

```cc
const int num_rows = SizeOfDimension(value, 0);
const int row_bytes = value->bytes / num_rows;
```

An attacker can craft a model such that `values`'s first dimension would be 0.

### Patches
We have patched the issue in GitHub commit
[5117e0851348065ed59c991562c0ec80d9193db2](https://github.com/tensorflow/tensorflow/commit/5117e0851348065ed59c991562c0ec80d9193db2).

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](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) 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.