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

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

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