chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2020-017.md

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+## TFSA-2020-017: Abort due to invalid splits in RaggedCountSparseOutput
+
+### CVE Number
+CVE-2020-15199
+
+### Impact
+The `RaggedCountSparseOutput` does not validate that the input arguments form a
+valid ragged tensor. In particular, there is no validation that the `splits`
+tensor has the minimum required number of elements. Code uses this quantity to
+[initialize a different data
+structure](https://github.com/tensorflow/tensorflow/blob/0e68f4d3295eb0281a517c3662f6698992b7b2cf/tensorflow/core/kernels/count_ops.cc#L241-L244):
+```cc
+    int num_batches = splits.NumElements() - 1;
+    auto per_batch_counts = BatchedMap<W>(num_batches);
+```
+
+Since `BatchedMap` is equivalent to a vector, it needs to have at least one
+element to not be `nullptr`. If user passes a `splits` tensor that is empty or
+has exactly one element, we get a `SIGABRT` signal raised by the operating
+system.
+
+### Vulnerable Versions
+TensorFlow 2.3.0.
+
+### Patches
+We have patched the issue in
+[3cbb917b4714766030b28eba9fb41bb97ce9ee02](https://github.com/tensorflow/tensorflow/commit/3cbb917b4714766030b28eba9fb41bb97ce9ee02)
+and will release a patch release.
+
+We recommend users to upgrade to TensorFlow 2.3.1.
+
+### 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 discovered through a variant analysis of [a
+vulnerability reported by members of the Aivul Team from Qihoo
+360](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/security/advisory/tfsa-2020-015.md).