GHSA-9x9p-qf8f-mvjg: LiquidJS's `{% render %}` tag silently bypasses per-render `ownPropertyOnly:true` via `Context.spawn()`

Summary Context.spawn() in liquidjs creates a child Context for the {% render %} tag but does not propagate the parent context's resolved ownPropertyOnly value. The new context re-derives ownPropertyOnly from opts.ownPropertyOnly (the instance-level option), silently discarding any RenderOptions.ownPropertyOnly override that was supplied to parseAndRender(). As a result, a developer who runs a Liquid instance with the backwards-compatible ownPropertyOnly:false and then locks down an untrusted render with parseAndRender(..., { ownPropertyOnly: true }) still leaks prototype-chain properties from inside any {% render %} partial. This is a distinct exploit surface from the previously identified array-filter variants (where, reject, group_by, find, find_index, has) — the underlying root cause in Context.spawn() is shared, but {% render %} is a separately reachable sink that needs no filter usage. Details The bug is in Context.spawn(): // src/context/context.ts:105-114 public spawn (scope = {}) { return new Context(scope, this.opts, { sync: this.sync, globals: this.globals, strictVariables: this.strictVariables // <-- ownPropertyOnly is missing here }, { renderLimit: this.renderLimit, memoryLimit: this.memoryLimit }) } The constructor resolves ownPropertyOnly as: // src/context/context.ts:47 this.ownPropertyOnly = renderOptions.ownPropertyOnly ?? opts.ownPropertyOnly Because spawn() passes a RenderOptions object with no ownPropertyOnly, the child context falls back to opts.ownPropertyOnly (the instance-level option), throwing away any per-render override that the parent context had applied. this.opts is the raw normalized instance options object; it is not mutated to reflect render-time overrides. The {% render %} tag at src/tags/render.ts:51-77 calls spawn() to build the partial's isolated scope: - render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> { const { liquid, hash } = this const filepath = (yield renderFilePath(this['file'], ctx, l