GHSA-7jvp-hj45-2f2m: Scriban: Template Writes to Arbitrary CLR Properties via `TypedObjectAccessor` (Mass Assignment + `private` / `init` / `internal` Setter Bypass)

<!-- obsidian --><h2 data-heading="Description">Description</h2> <p>When a host pushes a CLR object into a Scriban <code>TemplateContext</code> via the standard, documented pattern —</p> <pre><code class="language-csharp">var so = new ScriptObject(); so["user"] = currentUser; // direct CLR reference context.PushGlobal(so); </code></pre> <p>— <code>TypedObjectAccessor</code> exposes every public-getter property for <strong>both reading and writing</strong>, and writes land on the live host object and <strong>persist after <code>Render()</code> returns</strong>. The write path performs no <code>CanWrite</code> and no setter-visibility check, producing two related but distinct weaknesses:</p> <p><strong>(A) Mass assignment of public setters — CWE-915 (originally F-002).</strong> Any <code>{ get; set; }</code> property is writable from template code (<code>{{ user.is_admin = true }}</code>, <code>{{ order.total_price = 0 }}</code>). This is "surprising but technically consistent with the setter being public" — and crucially, Scriban offers <strong>no way to expose such a property read-only</strong>, because <code>MemberFilter</code> is read/write-symmetric.</p> <p><strong>(B) Access-modifier bypass — CWE-284 (originally F-007).</strong> Properties the developer <strong>deliberately</strong> restricted are also writable, because reflection ignores C# accessibility:</p> Declaration | Developer intent | Actual behavior -- | -- | -- { get; set; } | writable | writable (mass assignment — A) { get; private set; } | only the owning class writes | template writes freely { get; internal set; } | only the declaring assembly writes | template writes freely { get; init; } | immutable after construction (C# 9 language guarantee) | template writes freely post-construction <p>The <code>init</code>-only post-construction write — the highest false-positive risk — was explicitly confirmed against the shipped 7.2.1 package.</p> <h2 data-heading="Affected Versions">Affected Versions</