CVE-2026-34446: ONNX: Arbitrary File Read via ExternalData Hardlink Bypass in ONNX load

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-01 · updated 2026-06-17
Weakness: CWE-22

Description

Open Neural Network Exchange (ONNX) is an open standard for machine learning interoperability. Prior to version 1.21.0, there is an issue in onnx.load, the code checks for symlinks to prevent path traversal, but completely misses hardlinks because a hardlink looks exactly like a regular file on the filesystem. This issue has been patched in version 1.21.0.

Affected products

onnx: before 1.21.0 — fixed in 1.21.0

How to fix

Upgrade to a fixed version: onnx 1.21.0. Check the vendor advisory for mitigations.

References

https://github.com/onnx/onnx/commit/4755f8053928dce18a61db8fec71b69c74f786cb
https://github.com/onnx/onnx/security/advisories/GHSA-cmw6-hcpp-c6jp

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