Affected: onnx

Open Neural Network Exchange (ONNX) is an open standard for machine learning interoperability. From 1.9.0 before 1.22.0, onnx.version_converter.convert_version() can dereference a null pointer in Upsample_6_7::adapt_upsample_6_7() in onnx/version_converter/adapters/upsample_6_7.h when processing an untrusted model with an Upsample node that has zero inputs, causing an unrecoverable denial of service. This issue is fixed in version 1.22.0.

Affected: PyPI: onnx

### Summary

Null pointer dereference (SIGSEGV) in `Upsample_6_7::adapt_upsample_6_7()` (`onnx/version_converter/adapters/upsample_6_7.h:31`) when `convert_version()` processes a model with an Upsample node that has zero inputs. The adapter accesses `node->inputs()[0]->sizes()` without checking input count. 107-byte PoC crashes on Release build.

This is the same class of bug as the Cast adapter advisory (separate report) but in a different adapter, different file, and different operator.

### Details

The Upsample 6→7 adapter validates attributes but not inputs: ```cpp // upsample_6_7.h:20-33 void adapt_upsample_6_7(..., Node* node) const { ONNX_ASSERTM( node->hasAttribute(width_scale_symbol) && node->hasAttribute(height_scale_symbol), "...") // Attribute check PASSES

auto width_scale = node->f(width_scale_symbol); auto height_scale = node->f(height_scale_symbol);

auto input_shape = node->inputs()[0]->sizes(); // ^^^^^^^^^^^^^^^^^^^^ // OOB when inputs().size() == 0 → SIGSEGV } ```

The PoC has an Upsample node at opset 6 with the required `width_scale` and `height_scale` attributes but zero inputs. The attribute assertions pass, then `node->inputs()[0]` on an empty `ArrayRef`: - Release builds (`NDEBUG`): bounds-check assertion compiled out → reads garbage pointer → SIGSEGV - Debug builds: `assert(Index < Length)` at `array_ref.h:159` → SIGABRT

An Upsample node with zero inputs passes `graphProtoTo…