CVE-2026-49114
Received Received - Intake

Path Traversal in ONNX External Data Handling

Publication date: 2026-08-21

Last updated on: 2026-08-21

Assigner: Cybersecurity and Infrastructure Security Agency (CISA) U.S. Civilian Government

Description
In ONNX before 1.21.0, the 'save_external_data' function builds the external-data file path from the model's external_data location field and opens it for writing without 'O_NOFOLLOW/O_EXCL', after a non-atomic 'os.path.isfile()' check. A local attacker with write access to the directory where a victim serializes external data can deterministically pre-plant a symlink that is being followed, causing the victim's write to append to any file the victim can write, e.g. ~/.ssh/authorized_keys, cron files, or application configs. Fixed in 1.21.0.

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Meta Information

Published
2026-08-21
Last Modified
2026-08-21
Generated
2026-08-21
AI Q&A
2026-08-21
EPSS Evaluated
N/A
NVD
CVE-2026-49114
EUVD
EUVD-2026-63995

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
onnx onnx to 1.21.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-22 The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
CWE-367 The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
CWE-59 The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Attack-Flow Graph

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Executive Summary

This is a Time-of-Check Time-of-Use (TOCTOU) vulnerability in ONNX versions up to 1.20.1. It occurs in the 'save_external_data' function where a race condition exists between checking if a file exists and writing to it. An attacker can exploit this by pre-planting a symlink, causing the function to overwrite sensitive files like SSH keys or configuration files.

Detection Guidance

To detect this vulnerability, check if your ONNX library version is below 1.21.0. Run: pip show onnx or pip list | grep onnx. If the version is older, the system is vulnerable.

Impact Analysis

An attacker could overwrite critical system files such as ~/.ssh/authorized_keys, cron files, or application configs. This may lead to unauthorized access, system compromise, or data destruction. The vulnerability allows file overwrites and integrity breaches on systems where ONNX is used.

Compliance Impact

This vulnerability could lead to unauthorized file modifications, potentially violating data integrity and confidentiality requirements in GDPR and HIPAA. Unauthorized access or data breaches may result in non-compliance, legal penalties, or reputational damage.

Mitigation Strategies

Upgrade ONNX to version 1.21.0 or later immediately. Use pip install --upgrade onnx. Avoid using affected versions for serialization tasks until patched.

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