# 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.

- **Severity:** High 7.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 May 2026
- **Updated:** 12 May 2026
- **Also known as:** GHSA-7g5w-pq96-8c5w, PYSEC-2026-2477

## 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.

Weakness: CWE-94 (Improper Control of Generation of Code), CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-31253?

3 open source packages ship an affected version, including flash-attn and flash_attn.


| Package | Ecosystem | 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.

## Is CVE-2026-31253 being exploited?

There is no known exploitation of CVE-2026-31253 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31253 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-31253 in the wild and no public exploit code.

Affected packages and fixed versions:
- flash-attn (PyPI): affected all versions up to 2.8.3; no fix listed
- flash-attn (PyPI): affected all versions up to 2.8.3; no fix listed
- flash_attn (PyPI): affected all versions up to 2.8.3; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-31253/ (Markdown: https://insights.sbomify.com/CVE-2026-31253/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31253
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31253
- OSV: https://osv.dev/vulnerability/CVE-2026-31253

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-31253/
Summaries are generated and may contain mistakes; the official description above is the record.