CVE-2021-41220: Use after free in `CollectiveReduceV2`
First published: Fri Nov 05 2021(Updated: )
### Impact The [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: ```python import tensorflow as tf tf.raw_ops.CollectiveReduceV2( input=[], group_size=[-10, -10, -10], group_key=[-10, -10], instance_key=[-10], ordering_token=[], merge_op='Mul', final_op='Div') ``` This occurs due to the asynchronous computation and the fact that objects that have been `std::move()`d from are still accessed: ```cc auto done_with_cleanup = [col_params, done = std::move(done)]() { done(); col_params->Unref(); }; OP_REQUIRES_OK_ASYNC(c, FillCollectiveParams(col_params, REDUCTION_COLLECTIVE, /*group_size*/ c->input(1), /*group_key*/ c->input(2), /*instance_key*/ c->input(3)), done); ``` Here, `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. ### Patches We have patched the issue in GitHub commit [ca38dab9d3ee66c5de06f11af9a4b1200da5ef75](https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75). The 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. ### 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.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| pip/tensorflow-gpu | =2.6.0 | 2.6.1 |
| pip/tensorflow-cpu | =2.6.0 | 2.6.1 |
| pip/tensorflow | =2.6.0 | 2.6.1 |
| TensorFlow Keras | >=2.6.0<2.6.1 | |
| TensorFlow Keras | =2.7.0-rc0 | |
| TensorFlow Keras | =2.7.0-rc1 |
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Reference Links
- https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75
- https://github.com/tensorflow/tensorflow/security/advisories/GHSA-gpfh-jvf9-7wg5
- https://nvd.nist.gov/vuln/detail/CVE-2021-41220
- https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-629.yaml
- https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-827.yaml
- https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-412.yaml
- https://github.com/advisories/GHSA-gpfh-jvf9-7wg5 (Advisory)
Frequently Asked Questions
What is the severity of CVE-2021-41220?
CVE-2021-41220 is considered a moderate severity vulnerability due to the presence of a memory leak and use after free in TensorFlow.
How do I fix CVE-2021-41220?
To remediate CVE-2021-41220, upgrade your TensorFlow installation to version 2.6.1 or later.
What software versions are affected by CVE-2021-41220?
CVE-2021-41220 affects TensorFlow versions 2.6.0, 2.7.0-rc0, and 2.7.0-rc1.
What is the impact of CVE-2021-41220 on applications using TensorFlow?
The impact of CVE-2021-41220 includes potential application crashes and unexpected behavior due to memory management issues.
Is there a known exploit for CVE-2021-41220?
As of now, there is no widely publicized exploit available for CVE-2021-41220.
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