---
id: CVE-2021-41220
aliases:
  - GHSA-gpfh-jvf9-7wg5
  - BIT-tensorflow-2021-41220
  - PYSEC-2021-412
  - PYSEC-2021-629
  - PYSEC-2021-827
title: Use after free / memory leak in `CollectiveReduceV2`
summary: Use after free / memory leak in `CollectiveReduceV2`
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: tensorflow
product: tensorflow
ecosystem: pip
affected:
  - 'tensorflow >= 2.6.0, < 2.6.1'
  - 'tensorflow-cpu >= 2.6.0, < 2.6.1'
  - 'tensorflow-gpu >= 2.6.0, < 2.6.1'
patched:
  - tensorflow 2.6.1
  - tensorflow-cpu 2.6.1
  - tensorflow-gpu 2.6.1
published: '2021-11-10'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-gpfh-jvf9-7wg5'
references:
  - url: >-
      https://github.com/tensorflow/tensorflow/security/advisories/GHSA-gpfh-jvf9-7wg5
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-41220'
  - url: >-
      https://github.com/tensorflow/tensorflow/commit/ca38dab9d3ee66c5de06f11af9a4b1200da5ef75
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-629.yaml
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-827.yaml
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-412.yaml
  - url: 'https://github.com/tensorflow/tensorflow'
tags:
  - osv
  - pip
epss: 0.00211
epssPercentile: 0.10067
ingestedAt: '2026-07-08T18:25:49.753Z'
---

## Overview

### 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.


## Affected packages

- `tensorflow >= 2.6.0, < 2.6.1`
- `tensorflow-cpu >= 2.6.0, < 2.6.1`
- `tensorflow-gpu >= 2.6.0, < 2.6.1`

## Remediation

Upgrade to a patched release:

- `tensorflow 2.6.1`
- `tensorflow-cpu 2.6.1`
- `tensorflow-gpu 2.6.1`