CVE-2026-109153 MosaicML CVE debrief

Who should care

Defenders responsible for MosaicML Composer deployments should assess exposure and prioritize remediation. This vulnerability requires verification of affected versions and exposure, as well as implementation of compensating controls and monitoring.

Why it matters

CVE-2026-109153 is a medium-severity path traversal vulnerability in MosaicML Composer's Checkpoint Extraction component. Defenders should verify exposure, prioritize remediation, and implement compensating controls.

• Potential unauthorized file access or modification.
• Remote exploitation possible with medium CVSS score.
• Verification of affected versions and exposure required.
• Implementation of compensating controls and monitoring recommended.

Technical summary

The MosaicML Composer Checkpoint Extraction component is vulnerable to path traversal attacks due to improper handling of tarball extraction in the checkpoint.py file. This allows remote attackers to manipulate file paths, potentially leading to unauthorized file access or modification. The affected function, tarball.extractall, is located in composer/utils/checkpoint.py and affects MosaicML Composer versions up to 0.32.1. The vulnerability has a medium CVSS score, indicating a moderate level of risk. Defenders should review the affected component, assess exposure, and implement compensating controls to mitigate the risk.

Defensive priority

Medium priority due to the potential for remote exploitation and file system manipulation.

Recommended defensive actions

• Review and update MosaicML Composer to a version beyond 0.32.1 if available.
• Restrict access to the Checkpoint Extraction component to trusted users only.
• Monitor file system changes for anomalies.
• Implement additional file system security measures.
• Perform a thorough review of the affected component and its interactions with other systems.
• Verify the integrity of extracted files and implement measures to detect potential tampering.
• Conduct a risk assessment to determine the potential impact on the organization's assets and data.

Evidence notes

The vulnerability was detected in MosaicML Composer versions up to 0.32.1. The affected function is tarball.extractall in composer/utils/checkpoint.py. The CVE Program and NVD provide official records of this vulnerability.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.