ONNX: Malicious ONNX models can crash servers by exploiting unprotected object settings.

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

EPSS

• CVE-2026-34445: 0.29% estimated exploitation activity in the next 30 days; percentile 21.86 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The ExternalDataInfo class in ONNX was using Python’s setattr() function to load metadata (like file paths or data lengths) directly from an ONNX model file. The problem? It didn’t check if the "keys" in the file were valid. Because it blindly trusted the file, an attacker could craft a malicious model that overwrites internal object properties. Why its Dangerous Instant Crash DoS: An attacker can set the length property to a massive number like 9 petabytes. When the system tries to load the model, it attempts to allocate all that RAM at once, causing the server to crash or freeze Out of Memory. Access Bypass: By setting a negative offset -1, an attacker can trick the system into reading parts of a file it wasn't supposed to touch. Object Corruption: Attackers can even inject "dunder" attributes like class to change the object's type entirely, which could lead to more complex exploits. Fixed: https://github.com/onnx/onnx/pull/7751 object state corruption and DoS via…

Published by the source

1 Apr 2026, 21:10 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-538c-55jv-c5g9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-538c-55jv-c5g9

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# Patch Next advisory brief: CVE-2026-34445

Advisory: ONNX: Malicious ONNX models can crash servers by exploiting unprotected object settings.
IDs: CVE-2026-34445, GHSA-538c-55jv-c5g9
Record: https://patchnext.com/advisories/cve-2026-34445 (revision 2, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: onnx 1.21.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI onnx: affected <= 1.20.1; fixed in 1.21.0

## Suggested inspection (read-only)
- `python -m pip show onnx`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on onnx.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-538c-55jv-c5g9 (OSV record GHSA-538c-55jv-c5g9 lists affected ranges: PyPI onnx >=0 <1.21.0 (fixed))
- Verified: https://github.com/advisories/GHSA-538c-55jv-c5g9 (GitHub-reviewed advisory GHSA-538c-55jv-c5g9 lists affected ranges: PyPI onnx >=0 <=1.20.1)

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