{"id":"CVE-2021-41220","aliases":["BIT-tensorflow-2021-41220","GHSA-gpfh-jvf9-7wg5","PYSEC-2021-412","PYSEC-2021-629","PYSEC-2021-827"],"url":"https://o3.security/vulnerability/CVE-2021-41220","summary":"Use after free / memory leak in `CollectiveReduceV2`","details":"### Impact\nThe [async implementation](https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/collective_ops.cc#L604-L615) of `CollectiveReduceV2` suffers from a memory leak and a use after free:\n\n```python\nimport tensorflow as tf\n  \ntf.raw_ops.CollectiveReduceV2(\n  input=[],\n  group_size=[-10, -10, -10],\n  group_key=[-10, -10],\n  instance_key=[-10],\n  ordering_token=[],\n  merge_op='Mul',\n  final_op='Div')\n``` \n\nThis occurs due to the asynchronous computation and the fact that objects that have been `std::move()`d from are still accessed:\n\n```cc\nauto done_with_cleanup = [col_params, done = std::move(done)]() {\n  done();\n  col_params->Unref();\n};\nOP_REQUIRES_OK_ASYNC(c,\n                     FillCollectiveParams(col_params, REDUCTION_COLLECTIVE,\n                                          /*group_size*/ c->input(1),\n                                          /*group_key*/ c->input(2),\n                                          /*instance_key*/ c->input(3)),\n                     done);\n```\n\nHere, `done` is already moved from by the time `OP_REQUIRES_OK_ASYNC` macro needs to invoke it in case of errors. In this case, we get an undefined behavior, which can manifest via crashes, `std::bad_alloc` throws or just memory leaks.\n\n### Patches\nWe have patched the issue in GitHub commit [ca38dab9d3ee66c5de06f11af9a4b1200da5ef75](https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75).\n\nThe fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, as this version is the only one that is also affected.\n\n### For more information\nPlease 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.\n\n### Attribution\nThis vulnerability has been reported by members of the Aivul Team from Qihoo 360.\n","published":"2021-11-05T23:15:08.350Z","modified":"2026-08-07T16:57:40.334209Z","cvss":{"score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":1,"affectedPackages":[{"ecosystem":"PyPI","name":"tensorflow","fixedVersion":"2.6.1"},{"ecosystem":"PyPI","name":"tensorflow-cpu","fixedVersion":"2.6.1"},{"ecosystem":"PyPI","name":"tensorflow-gpu","fixedVersion":"2.6.1"}],"fix":{"url":"https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75","label":"tensorflow/tensorflow@ca38dab"},"references":[{"type":"FIX","url":"https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75"},{"type":"FIX","url":"https://github.com/tensorflow/tensorflow/security/advisories/GHSA-gpfh-jvf9-7wg5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-41220"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-629.yaml"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-827.yaml"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-412.yaml"},{"type":"PACKAGE","url":"https://github.com/tensorflow/tensorflow"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T16:57:40.334209Z"}}