# CVE-2026-31221: Lightning AI PyTorch Lightning insecure deserialization in checkpoint loading

Source: https://junglewise.ai/threats/cve-2026-31221-lightning-ai-pytorch-lightning-insecure-deserialization-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-12. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

CVE-2026-31221 · Severity: high · CVSS 7.8 · Published 2026-05-12

PyTorch Lightning, a popular framework for training AI models, contains a security flaw in how it loads saved model checkpoints. If a user is tricked into loading a maliciously crafted checkpoint file, an attacker can execute arbitrary commands on the user's computer. This could lead to full system compromise, data theft, or unauthorized access to research environments.

Technologies: [lightning (PyPI)](https://junglewise.ai/threats/technologies/lightning), [pytorch-lightning (PyPI)](https://junglewise.ai/threats/technologies/pytorch-lightning). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-31221 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31221 being exploited in the wild.

**How severe is CVE-2026-31221?** High severity, with a CVSS score of 7.8, published 12 May 2026.

**Which products and versions are affected?** lightning (PyPI) ECOSYSTEM:introduced=0,last_affected=2.6.0; pytorch-lightning (PyPI) <= 2.6.0, ECOSYSTEM:introduced=0,last_affected=2.6.0.

**Is there a fix for CVE-2026-31221?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-31221 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-31221?** Check whether you run lightning (PyPI) or pytorch-lightning (PyPI) 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.

## Technical details

An insecure deserialization vulnerability (CWE-502) exists in PyTorch Lightning versions <= 2.6.0 within the checkpoint loading mechanism. The 'LightningModule.load_from_checkpoint()' method internally calls 'torch.load()' without enabling the 'weights_only=True' security restriction. This allows the Pickle module to deserialize arbitrary Python objects. An attacker can exploit this by providing a crafted checkpoint file; when a user loads this file, it triggers arbitrary code execution. The attack requires the victim to load the malicious file (User Interaction), typically in a local environment.

## Affected products

- Lightning-AI pytorch-lightning <= 2.6.0

## Identifiers

- CVE-2026-31221
- GHSA-75m9-98v2-hjpm
- PYSEC-2026-3043
- PYSEC-2026-3972

## Timeline

- 2026-05-12: disclosed
- 2026-05-12: advisory: NVD publication date
- 2026-05-18: other: GitHub Advisory reviewed

## References

- [https://github.com/Lightning-AI/pytorch-lightning](https://github.com/Lightning-AI/pytorch-lightning)
- [https://www.notion.so/CVE-2026-31221-35d1e1393188815f8db7c4fd08076639](https://www.notion.so/CVE-2026-31221-35d1e1393188815f8db7c4fd08076639)

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- [PYSEC-2026-3974 - Remote code execution in pytorch lightning](https://junglewise.ai/threats/cve-2024-5452-remote-code-execution-in-pytorch-lightning)