ONNX: Denial of service via unchecked expansion of packed sub-byte tensors in ONNX Python APIs

Exploitation

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

CVSS

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

EPSS

• CVE-2026-115922: 0.13% estimated exploitation activity in the next 30 days; percentile 2.71 (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 ONNX's Python tensor-materialization helpers could allocate memory according to attacker-controlled tensor dimensions without verifying that a packed sub-byte payload contained the declared number of elements. A very small model could therefore cause a disproportionately large allocation when an application called `onnx.numpy_helper.to_array()` or constructed `onnx.reference.ReferenceEvaluator` with the model. The issue affected `UINT2`, `INT2`, `UINT4`, `INT4`, and `FLOAT4E2M1` tensors stored in either `raw_data` or packed `int32_data`.

Technical details The vulnerable `_unpack_2bit()` and `_unpack_4bit()` paths first allocated a small array based on the available packed bytes, then resized it to the shape declared in `TensorProto.dims`. They did not first confirm that the payload encoded enough logical elements for that shape. For example, the reporter demonstrated a 66-byte model containing one packed byte and a declared dimension of 700,000,000. The model passed…

Published by the source

28 Oct 2026, 21:16 UTC

Last modified by the source

28 Oct 2026, 21:30 UTC

Source last checked

29 Oct 2026, 06:10 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-q69g-f4f5-v8m7

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-q69g-f4f5-v8m7

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# Patch Next advisory brief: CVE-2026-115922

Advisory: ONNX: Denial of service via unchecked expansion of packed sub-byte tensors in ONNX Python APIs
IDs: CVE-2026-115922, GHSA-q69g-f4f5-v8m7
Record: https://patchnext.com/advisories/cve-2026-115922 (revision 2, source checked 29 Oct 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: onnx 1.22.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI onnx: affected < 1.22.0; fixed in 1.22.0

## 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://github.com/advisories/GHSA-q69g-f4f5-v8m7 (GitHub-reviewed advisory GHSA-q69g-f4f5-v8m7 lists affected ranges: PyPI onnx >=0 <=1.21.0)
- Verified: https://osv.dev/vulnerability/GHSA-q69g-f4f5-v8m7 (OSV record GHSA-q69g-f4f5-v8m7 lists affected ranges: PyPI onnx >=0 <1.22.0 (fixed))

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