GHSA-w74j-v8xh-3w5h Reference binding to nullptr in unicode encoding

• PyPI tensorflow: < 2.3.4 → fixed in 2.3.4 • PyPI tensorflow: >= 2.4.0, < 2.4.3 → fixed in 2.4.3 • PyPI tensorflow: >= 2.5.0, < 2.5.1 → fixed in 2.5.1 • PyPI tensorflow-cpu: < 2.3.4 → fixed in 2.3.4 • PyPI tensorflow-cpu: >= 2.4.0, < 2.4.3 → fixed in 2.4.3 • PyPI tensorflow-cpu: >= 2.5.0, < 2.5.1 → fixed in 2.5.1 • PyPI tensorflow-gpu: < 2.3.4 → fixed in 2.3.4 • PyPI tensorflow-gpu: >= 2.4.0, < 2.4.3 → fixed in 2.4.3 • PyPI tensorflow-gpu: >= 2.5.0, < 2.5.1 → fixed in 2.5.1

Impact An attacker can cause undefined behavior via binding a reference to null pointer in `tf.raw_ops.UnicodeEncode`: ```python 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: ```cc const Tensor& input_splits = context->input(1); const auto input_splits_flat = input_splits.flat(); 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.