CVE-2026-31221 PyTorch Lightning load_from_checkpoint has an insecure checkpoint deserialization
Attackers can execute arbitrary code by tricking users into loading malicious checkpoint files in PyTorch Lightning due to insecure deserialization.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-31221?
CVE-2026-31221 is a high-severity unsafe deserialization vulnerability in n/a, published on 12 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
PyTorch-Lightning versions 2.6.0 and earlier contain an insecure deserialization vulnerability (CWE-502) in the checkpoint loading mechanism. The LightningModule.load_from_checkpoint() method, which is commonly used to load saved model states, internally calls torch.load() without setting the security-restrictive weights_only=True parameter. This default behavior allows the deserialization of arbitrary Python objects via the Pickle module. A remote attacker can exploit this by providing a maliciously crafted checkpoint file, leading to arbitrary code execution on the victim's system when the file is loaded.
Weakness: CWE-502
Which versions are affected by CVE-2026-31221?
4 open source packages ship an affected version, including pytorch-lightning and lightning. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pytorch-lightning PyPI | All versions to 2.6.0 | None |
pytorch-lightning PyPI | All versions to 2.6.0 | None |
pytorch-lightning PyPI | All versions to 2.6.0 | None |
lightning PyPI | All versions to 2.6.0 | None |
Products include Lightningai Pytorch Lightning.
How do I fix CVE-2026-31221?
No fix has been published for CVE-2026-31221 yet. Limit exposure of the affected software until one is available.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-31221 being exploited?
There is no known exploitation of CVE-2026-31221 in the wild and no public exploit code.
Other vulnerabilities in n/a
- CVE-2024-5452 RCE via Property/Class Pollution in lightning-ai/pytorch-lightning
- CVE-2026-44484 Compromise of PyTorch Lightning PyPi Package Versions
- CVE-2024-8019 Arbitrary File Write/Overwrite in lightning-ai/pytorch-lightning
- CVE-2024-5980 Arbitrary File Write via /v1/runs API endpoint in lightning-ai/pytorch-lightning
- CVE-2026-58659 PyTorch Lightning Arbitrary Code Execution via _instantiator Hyperparameter
Sources
Also known as GHSA-75m9-98v2-hjpm, PYSEC-2026-3043, PYSEC-2026-3972, UBUNTU-CVE-2026-31221.