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

> Attackers can read arbitrary files by using hardlinks to bypass symlink checks in ONNX model loading, affecting ML pipelines using the library.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** AZL-81986, DEBIAN-CVE-2026-34446, ECHO-76fb-f78f-1fbe, GHSA-cmw6-hcpp-c6jp, PYSEC-2026-2241, UBUNTU-CVE-2026-34446

## What is CVE-2026-34446?

CVE-2026-34446 is a medium-severity path traversal vulnerability in onnx, published on 1 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-61 (UNIX Symbolic Link (Symlink) Following), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-34446?

3 open source packages ship an affected version, including onnx. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `onnx` | PyPI | All versions | 1.21.0 |
| `onnx` | PyPI | All versions | 1.21.0 |
| `onnx` | PyPI | All versions | 1.21.0 |

Products: Linuxfoundation Onnx.

## How do I fix CVE-2026-34446?

Upgrade onnx to 1.21.0 or later.

## Is CVE-2026-34446 being exploited?

There is no known exploitation of CVE-2026-34446 in the wild and no public exploit code.

## Other vulnerabilities in onnx

- [CVE-2025-51480](https://insights.sbomify.com/CVE-2025-51480/): Path traversal in n/a (high 8.8)
- [CVE-2024-5187](https://insights.sbomify.com/CVE-2024-5187/): Arbitrary File Overwrite in download_model_with_test_data in onnx/onnx (high 8.8)
- [CVE-2026-27489](https://insights.sbomify.com/CVE-2026-27489/): ONNX: Path Traversal via Symlink (high 8.7)
- [CVE-2026-34445](https://insights.sbomify.com/CVE-2026-34445/): ONNX: Malicious ONNX models can crash servers by exploiting unprotected object settings. (high 8.6)
- [CVE-2026-28500](https://insights.sbomify.com/CVE-2026-28500/): ONNX Untrusted Model Repository Warnings Suppressed by silent=True in onnx.hub.load() — Silent Supply-Chain Attack (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34446 and fix it if it is affected.

What it is: CVE-2026-34446 is a medium-severity path traversal vulnerability in onnx, published on 1 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-34446 in the wild and no public exploit code.

Affected packages and fixed versions:
- onnx (PyPI): affected all versions; fixed in 1.21.0
- onnx (PyPI): affected all versions; fixed in 1.21.0
- onnx (PyPI): affected all versions; fixed in 1.21.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-34446/ (Markdown: https://insights.sbomify.com/CVE-2026-34446/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34446
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34446
- OSV: https://osv.dev/vulnerability/CVE-2026-34446

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34446/
Summaries are generated and may contain mistakes; the official description above is the record.