1## TFSA-2021-055: Reference binding to null in `ParameterizedTruncatedNormal` 2 3### CVE Number 4CVE-2021-29568 5 6### Impact 7An attacker can trigger undefined behavior by binding to null pointer in 8`tf.raw_ops.ParameterizedTruncatedNormal`: 9 10```python 11import tensorflow as tf 12 13shape = tf.constant([], shape=[0], dtype=tf.int32) 14means = tf.constant((1), dtype=tf.float32) 15stdevs = tf.constant((1), dtype=tf.float32) 16minvals = tf.constant((1), dtype=tf.float32) 17maxvals = tf.constant((1), dtype=tf.float32) 18 19tf.raw_ops.ParameterizedTruncatedNormal( 20 shape=shape, means=means, stdevs=stdevs, minvals=minvals, maxvals=maxvals) 21``` 22 23This is because the 24[implementation](https://github.com/tensorflow/tensorflow/blob/3f6fe4dfef6f57e768260b48166c27d148f3015f/tensorflow/core/kernels/parameterized_truncated_normal_op.cc#L630) 25does not validate input arguments before accessing the first element of `shape`: 26 27```cc 28int32 num_batches = shape_tensor.flat<int32>()(0); 29``` 30 31If `shape` argument is empty, then `shape_tensor.flat<T>()` is an empty array. 32 33### Patches 34We have patched the issue in GitHub commit 35[5e52ef5a461570cfb68f3bdbbebfe972cb4e0fd8](https://github.com/tensorflow/tensorflow/commit/5e52ef5a461570cfb68f3bdbbebfe972cb4e0fd8). 36 37The fix will be included in TensorFlow 2.5.0. We will also cherrypick this 38commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 392.1.4, as these are also affected and still in supported range. 40 41### For more information 42Please consult [our security 43guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for 44more information regarding the security model and how to contact us with issues 45and questions. 46 47### Attribution 48This vulnerability has been reported by Ying Wang and Yakun Zhang of Baidu 49X-Team. 50