Reference binding to nullptr in unicode encoding

Impact

An attacker can cause undefined behavior via binding a reference to null pointer in tf.raw_ops.UnicodeEncode:

import tensorflow as tf
from tensorflow.python.ops import gen_string_ops

gen_string_ops.unicode_encode(
  input_values=[],
  input_splits=[],
  output_encoding='UTF-8',
  errors='ignore',
  replacement_char='a')

The implementation reads the first dimension of the input_splits tensor before validating that this tensor is not empty:

  const Tensor& input_splits = context->input(1);
  const auto input_splits_flat = input_splits.flat<SPLITS_TYPE>();
  TensorShape output_shape({input_splits.dim_size(0) - 1});

Patches

We have patched the issue in GitHub commit 2e0ee46f1a47675152d3d865797a18358881d7a6.

The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, 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.