Reference binding to `nullptr` in `tf.ragged.cross`

Impact

The shape inference code for tf.ragged.cross has an undefined behavior due to binding a reference to nullptr. In the following scenario, this results in a crash:

import tensorflow as tf
  
@tf.function                 
def test():     
  y = tf.ragged.cross([tf.ragged.constant([['1']]),'2'])
  return y                   
                             
test()        

Patches

We have patched the issue in GitHub commit fa6b7782fbb14aa08d767bc799c531f5e1fb3bb8.

The fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, TensorFlow 2.5.2, and TensorFlow 2.4.4, 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.