CVE-2026-31253 flash-attention contains an insecure deserialization vulnerability in its checkpoint loading mechanism
An attacker can execute arbitrary code by tricking a user into loading a malicious checkpoint file in the flash-attention training framework.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-31253?
CVE-2026-31253 is a high-severity unsafe deserialization vulnerability in n/a, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The flash-attention training framework thru commit e724e2588cbe754beb97cf7c011b5e7e34119e62 (2025-13-04) contains an insecure deserialization vulnerability (CWE-502) in its checkpoint loading mechanism. The load_checkpoint() function in checkpoint.py and the checkpoint loading code in eval.py use torch.load() without enabling the security-restrictive weights_only=True parameter. This allows the deserialization of arbitrary Python objects via the pickle module. An attacker can exploit this by providing a maliciously crafted checkpoint file. When a victim loads this checkpoint during model warmstarting or evaluation, arbitrary code is executed on the victim's system.
Which versions are affected by CVE-2026-31253?
3 open source packages ship an affected version, including flash-attn and flash_attn.
| Package | Affected | Fixed in |
|---|---|---|
flash-attn PyPI | All versions to 2.8.3 | None |
flash-attn PyPI | All versions to 2.8.3 | None |
flash_attn PyPI | All versions to 2.8.3 | None |
How do I fix CVE-2026-31253?
No fix has been published for CVE-2026-31253 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-2026-31253 being exploited?
There is no known exploitation of CVE-2026-31253 in the wild and no public exploit code.
Sources
Also known as GHSA-7g5w-pq96-8c5w, PYSEC-2026-2477.