PYSEC-2026-506

### Summary

python-statemachine 3.1.2 evaluates `<data expr="...">` attributes in SCXML documents using Python's `eval()`. Any application that passes attacker-controlled SCXML content to `SCXMLProcessor` is vulnerable to arbitrary code execution in the context of the hosting process.

### Details

`SCXMLProcessor.parse_scxml_file()` processes SCXML documents and evaluates `<data>` element `expr` attributes via the following call chain:

``` SCXMLProcessor.parse_scxml_file() SCXMLProcessor.process_definition() create_datamodel_action_callable() _create_dataitem_callable() _eval() eval() ```

`_eval()` calls Python's built-in `eval()` directly on the expression string without sandboxing or restriction.

### PoC

``` 1. Install: pip install python-statemachine==3.1.2

2. Create an SCXML file containing: <data id="x" expr="__import__('pathlib').Path('marker.txt').write_text('pwned')"/>

3. Run: SCXMLProcessor.parse_scxml_file(DATA_EXPR_CHART) SCXMLProcessor.start() 4. During start(), <data expr> reaches _eval(), which calls eval().

5. Result: data_marker_before_start: False data_marker_after_start: True success: True ```

### Impact

This is an eval injection vulnerability (CWE-95). Remote or local code execution depending on whether the consuming application accepts SCXML content from remote users, uploaded files, configuration, plugins, or other untrusted sources.