Summary
ONNX: Out-of-bounds read in ConvTranspose shape inference via undersized weight rank
ONNX ConvTranspose shape inference performed an out-of-bounds read when the weight tensor had fewer than three dimensions and the model did not provide a kernel_shape attribute.
The inference function derived an empty effective_kernel_shape vector from the undersized weight tensor, then indexed that vector once for each spatial dimension of the input tensor. A crafted model passed onnx.checker.check_model() and caused SIGSEGV when passed to onnx.shape_inference.infer_shapes().
Technical details
For an input shape such as [1, 1, 5], shape inference computes one spatial input dimension. A weight shape such as [1, 3] has no spatial dimensions, so deriving kernel_shape from dimensions 2 onward produces an empty vector. The output loop nevertheless accesses effective_kernel_shape[0].
The defect affected both the older convTransposeShapeInference_opset11() path and the then-current ConvTranspose inference implementation.
Affected versions
- Affected: ONNX 1.2.1 through 1.21.0
- Patched: ONNX 1.22.0
Severity
The vulnerable ONNX component processes the malicious model through a local library API or file boundary and is not itself bound to a network stack. Applications that expose ONNX model processing over a network should calculate an Environmental score with Modified Attack Vector set to Network.
Impact
An application that performs shape inference on an untrusted model can be terminated, causing denial of service. The observed result was a deterministic process crash. No confidentiality or integrity impact was demonstrated.
A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.
CVE-2026-115920 has a CVSS score of 6.2 (Medium). The vector is requires local access, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.22.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Upgrade to ONNX 1.22.0 or later. The fix rejects input and weight tensors with fewer than three dimensions before deriving the spatial kernel shape.
- Fix: onnx/onnx#7997
- Commit:
2ec288908
The original malformed model was re-tested against the published ONNX 1.23.2 wheel and correctly raises InferenceError.
Frequently Asked Questions
- What is CVE-2026-115920? CVE-2026-115920 is a medium-severity out-of-bounds read vulnerability in onnx (pip), affecting versions >= 1.2.1, <= 1.21.0. It is fixed in 1.22.0. A read operation accesses a memory location beyond the intended buffer boundary.
- How severe is CVE-2026-115920? CVE-2026-115920 has a CVSS score of 6.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of onnx are affected by CVE-2026-115920? onnx (pip) versions >= 1.2.1, <= 1.21.0 is affected.
- Is there a fix for CVE-2026-115920? Yes. CVE-2026-115920 is fixed in 1.22.0. Upgrade to this version or later.
- Is CVE-2026-115920 exploitable, and should I be worried? Whether CVE-2026-115920 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-115920 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-115920? Upgrade
onnxto 1.22.0 or later.