GHSA-3jhf-gxhr-q4cx

### Summary

When parsing shader nodes in a MTLX file, the MaterialXCore code accesses a potentially null pointer, which can lead to crashes with maliciously crafted files.

### Details

In `src/MaterialXCore/Material.cpp`, in function `getShaderNodes`, the following code fetches the output nodes for a given `nodegraph` input node:

```cpp // SNIP... else if (input->hasNodeGraphString()) { // Check upstream nodegraph connected to the input. // If no explicit output name given then scan all outputs on the nodegraph. ElementPtr parent = materialNode->getParent(); NodeGraphPtr nodeGraph = parent->getChildOfType<NodeGraph>(input->getNodeGraphString()); if (!nodeGraph) { continue; } vector<OutputPtr> outputs; if (input->hasOutputString()) { outputs.push_back(nodeGraph->getOutput(input->getOutputString())); // <--- null ptr is returned } else { outputs = nodeGraph->getOutputs(); } for (OutputPtr output : outputs) { NodePtr upstreamNode = output->getConnectedNode(); // <--- CRASHES HERE if (upstreamNode && !shaderNodeSet.count(upstreamNode)) { if (!target.empty() && !upstreamNode->getNodeDef(target)) { continue; } shaderNodeVec.push_back(upstreamNode); shaderNodeSet.insert(upstreamNode); } } } } // SNIP... ```

The issues arise because the `nodeGraph->getOutput(input->getOutputString())` call can return a null pointer, therefore when trying to call `output->getConnectedNode()`, this results in a crash .

### PoC

Please download `nullptr_getshadernodes.mltx` from the following link:

https://github.com/ShielderSec/poc/tree/main/CVE-2025-53010

`build/bin/MaterialXView --material nullptr_getshadernodes.mtlx`

### Impact

An attacker could intentionally crash a target program that uses OpenEXR by sending a malicious MTLX file.