chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-133.md

@@ -0,0 +1,39 @@
+## TFSA-2021-133: Reference binding to nullptr and heap OOB in binary cwise ops
+
+### CVE Number
+CVE-2021-37659
+
+### Impact
+An attacker can cause undefined behavior via binding a reference to null pointer
+in all binary cwise operations that don't require broadcasting (e.g., gradients
+of binary cwise operations):
+
+```python
+import tensorflow as tf
+
+tf.raw_ops.SqrtGrad(y=[4, 16],dy=[])
+```
+
+The
+[implementation](https://github.com/tensorflow/tensorflow/blob/84d053187cb80d975ef2b9684d4b61981bca0c41/tensorflow/core/kernels/cwise_ops_common.h#L264)
+assumes that the two inputs have exactly the same number of elements but does
+not check that. Hence, when the eigen functor executes it triggers heap OOB
+reads and undefined behavior due to binding to nullptr.
+
+### Patches
+We have patched the issue in GitHub commit
+[93f428fd1768df147171ed674fee1fc5ab8309ec](https://github.com/tensorflow/tensorflow/commit/93f428fd1768df147171ed674fee1fc5ab8309ec).
+
+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](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) 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.