# CVE-2026-10043: MosaicML Composer insecure deserialization in checkpoint parsing

Source: https://junglewise.ai/threats/cve-2026-10043-mosaicml-composer-insecure-deserialization-in-checkpoint-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-10043 · Severity: high · CVSS 7.8 · Published 2026-06-24

MosaicML Composer is an open-source library used for training machine learning models. A security vulnerability in how the software handles 'checkpoint' files could allow an attacker to execute malicious code on a user's system. To exploit this, an attacker would need to trick a user into opening a specially crafted malicious file or visiting a compromised webpage. Successful exploitation could lead to a full system compromise or unauthorized access to sensitive training data.

## Quick answers

**Is CVE-2026-10043 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-10043 being exploited in the wild.

**How severe is CVE-2026-10043?** High severity, with a CVSS score of 7.8, published 24 June 2026.

**Which products and versions are affected?** MosaicML Composer 0.32.1.

**Is there a fix for CVE-2026-10043?** A patch was published on 2026-04-29: Fix committed to GitHub repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-10043 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-10043?** Check whether anything you run is named in the advisory. 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

A deserialization vulnerability (CWE-502) exists in MosaicML Composer within the checkpoint parsing logic. The root cause is the use of the Python 'pickle' module to process user-supplied checkpoint data without adequate validation or restricted global access. An attacker can craft a malicious serialized object that, when unpickled, executes arbitrary commands. While categorized as remote code execution, the attack vector is local (AV:L) requiring user interaction (UI:R), such as loading a malicious checkpoint file. The vulnerability has been addressed in a commit that implements a restricted 'Unpickler' using a whitelist of safe globals (_RESUMPTION_SAFE_GLOBALS).

## Affected products

- MosaicML Composer 0.32.1

## Timeline

- 2026-02-12: disclosed: Vulnerability reported to vendor
- 2026-04-29: patched: Fix committed to GitHub repository
- 2026-06-24: advisory: Coordinated public release of advisory

## References

- [https://github.com/mosaicml/composer/commit/6405188805a0054b4551ec49e4919c54c971d0e8](https://github.com/mosaicml/composer/commit/6405188805a0054b4551ec49e4919c54c971d0e8)
- [https://www.zerodayinitiative.com/advisories/ZDI-26-384/](https://www.zerodayinitiative.com/advisories/ZDI-26-384/)