# CVE-2021-37668: TensorFlow UnravelIndex division by zero

Source: https://junglewise.ai/threats/cve-2021-37668-tensorflow-unravelindex-division-by-zero  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-08-12. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2021-37668 · Severity: low · CVSS 3.1 · Published 2021-08-12

TensorFlow's UnravelIndex operation, used for index manipulation in machine learning models, contains a flaw that allows an attacker to crash applications by providing specially crafted input containing zero values. This causes a denial-of-service condition, making services unavailable until restarted.

Technologies: [Google TensorFlow](https://junglewise.ai/threats/technologies/tensorflow), [tensorflow (PyPI)](https://junglewise.ai/threats/technologies/pypi-tensorflow), [tensorflow-cpu (PyPI)](https://junglewise.ai/threats/technologies/tensorflow-cpu), [tensorflow-gpu (PyPI)](https://junglewise.ai/threats/technologies/tensorflow-gpu). Vendors: [Google](https://junglewise.ai/threats/vendors/google), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2021-37668 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-37668 being exploited in the wild.

**How severe is CVE-2021-37668?** Low severity, with a CVSS score of 3.1, published 12 August 2021.

**Which products and versions are affected?** Google TensorFlow versions prior to 2.3.4; 2.4.0–2.4.2; 2.5.0; tensorflow (PyPI) GIT:introduced=0,fixed=a776040a5e7ebf76eeb7eb923bf1ae417dd4d233|ECOSYSTEM:introduced=2.3.0,fixed=2.3.4,introduced=2.4.0,fixed=2.4.3; tensorflow-cpu (PyPI) GIT:introduced=0,fixed=a776040a5e7ebf76eeb7eb923bf1ae417dd4d233|ECOSYSTEM:introduced=2.3.0,fixed=2.3.4,introduced=2.4.0,fixed=2.4.3; tensorflow-gpu (PyPI) GIT:introduced=0,fixed=a776040a5e7ebf76eeb7eb923bf1ae417dd4d233|ECOSYSTEM:introduced=2.3.0,fixed=2.3.4,introduced=2.4.0,fixed=2.4.3.

**Is there a fix for CVE-2021-37668?** Yes. tensorflow (PyPI): upgrade to 2.4.3 or later; tensorflow-cpu (PyPI): upgrade to 2.4.3 or later; tensorflow-gpu (PyPI): upgrade to 2.4.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2021-37668 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2021-37668?** Check whether you run Google TensorFlow, tensorflow (PyPI), tensorflow-cpu (PyPI) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- tensorflow (PyPI): upgrade to 2.4.3 or later

  ```sh
  pip install "tensorflow>=2.4.3"
  ```

- tensorflow-cpu (PyPI): upgrade to 2.4.3 or later

  ```sh
  pip install "tensorflow-cpu>=2.4.3"
  ```

- tensorflow-gpu (PyPI): upgrade to 2.4.3 or later

  ```sh
  pip install "tensorflow-gpu>=2.4.3"
  ```


## Technical details

The vulnerability is a division-by-zero error (CWE-369) in tf.raw_ops.UnravelIndex. The root cause is missing input validation: the operation does not verify that the dims tensor is non-empty or that none of its elements are zero before performing mathematical operations that divide by dim values. An attacker can trigger the flaw by calling UnravelIndex with dims containing a 0 value (e.g., dims=[1,0,2]). No authentication is required; the operation is network-reachable in applications serving TensorFlow models. The impact is denial of service through application crash. Patches are available in TensorFlow 2.3.4, 2.4.3, 2.5.1, and 2.6.0.

## Affected products

- Google TensorFlow versions prior to 2.3.4; 2.4.0–2.4.2; 2.5.0
- Google TensorFlow CPU versions prior to 2.3.4; 2.4.0–2.4.2; 2.5.0
- Google TensorFlow GPU versions prior to 2.3.4; 2.4.0–2.4.2; 2.5.0

## Identifiers

- CVE-2021-37668
- GHSA-2wmv-37vq-52g5
- PYSEC-2021-290
- PYSEC-2021-581
- PYSEC-2021-779

## Timeline

- 2021-08-12: disclosed: NVD publication
- 2021-08-25: advisory: GitHub security advisory published
- 2021-08-12: patched: Fix committed in TensorFlow; patches released in 2.3.4, 2.4.3, 2.5.1, and included in 2.6.0

## References

- [https://github.com/tensorflow/tensorflow/security/advisories/GHSA-2wmv-37vq-52g5](https://github.com/tensorflow/tensorflow/security/advisories/GHSA-2wmv-37vq-52g5)

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