The vulnerability stems from improper enforcement of Restricted Python in Chameleon (five.pt) when processing templates. The core issue lies in template compilation and expression evaluation logic, where the sandboxing mechanism was not applied correctly. While the exact functions are inferred (due to lack of patch details), the five.pt engine's compile method and expression evaluator are the most likely candidates, as they directly handle untrusted template code. Confidence is medium because the analysis relies on component roles rather than explicit code/commit evidence.