The vulnerability description explicitly links XSS exploitation to templates using {{this}} with user-supplied primitive values. This indicates the root cause is in the template engine's handling of the {{this}} special variable when the context is a non-object primitive. The HTMLBars subsystem (Ember's template engine) would be responsible for rendering this value without proper escaping. While exact file paths aren't provided in available resources, Ember's architecture places template rendering logic in HTMLBars packages. The confidence is high because the attack vector directly maps to template engine behavior described in advisories, even without specific commit diffs.