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Medium

ONNX: Arbitrary File Read via ExternalData Hardlink Bypass in ONNX load

  • Disclosed: 01.04.2026
  • Updated: 11.10.2026 15:17

Summary

The issue is in onnx.load — the code checks for symlinks to prevent path traversal, but completely misses hardlinks, which is the problem, since a hardlink looks exactly like a regular file on the filesystem.

The Real Problem

The validator in onnx/checker.cc only calls is_symlink() and never checks the inode or st_nlink, so a hardlink walks right through every security check without any issues.

Impact

Especially dangerous in AI supply chain scenarios like HuggingFace — a single malicious model is enough to silently steal secrets from the victim's machine without them noticing anything.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) onnx < 1.21.0 1.21.0

References

CVSS score 4.7/10
CVSS vector
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
Weakness (CWE)
CWE-22, CWE-61
Platform
Python (PyPI)
Package
onnx
Disclosed
01.04.2026
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-2241 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-cmw6-hcpp-c6jp - CC BY 4.0

Vulnerability history: onnx

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (13) in the archive
Total entries
13
First → latest
01.2023 07.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 1
  • High 7
  • Medium 4
  • Low 1

Disclosures per year

Severity:
  1. ONNX: TOCTOU arbitrary file read/write in save_external_dat
    High · 7.1 CVE-2026-49114 < 1.21.0 1.21.0
  2. ONNX: Arbitrary File Read via ExternalData Hardlink Bypass in ONNX load this entry
    Medium · 4.7 CVE-2026-34446 < 1.21.0 1.21.0
  3. ONNX: Malicious ONNX models can crash servers by exploiting unprotected object settings.
    High · 8.6 CVE-2026-34445 < 1.21.0 1.21.0
  4. onnx Vulnerable to Path Traversal via Symlink
    High CVE-2026-27489 < 1.21.0 1.21.0
  5. ONNX Untrusted Model Repository Warnings Suppressed by silent=True in onnx.hub.load() — Silent Supply-Chain Attack
    High · 8.6 CVE-2026-28500 < 1.21.0rc1 1.21.0rc1
  6. A vulnerability in the `download_model` function of the onnx/onnx framework, before and including version 1.16.1, allows for arbitrary file overwrite due to inadequate prevention of path traversal att
    Critical · 9.1 CVE-2024-7776 < 1.16.2 1.16.2
  7. onnx allows Arbitrary File Overwrite in download_model_with_test_data
    High · 8.8 CVE-2024-5187 < 1.16.2 1.16.2
  8. Onnx Directory Traversal vulnerability
    High · 7.5 CVE-2024-27318 < 1.16.0 1.16.0
  9. Versions of the package onnx before 1.13.0 are vulnerable to Directory Traversal as the external_data field of the tensor proto can have a path to the file which is outside the model current directory
    High · 7.5 CVE-2022-25882 < 1.13.0 1.13.0

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