CVE-2026-71291: Bolt CMS Server-Side Template Injection via Unsandboxed allow_twig Field Rendering

Bolt CMS renders content field values through Twig's full application-level Environment with no SandboxExtension registered anywhere in the codebase. In src/Entity/Field.php, getTwigValue() calls shouldBeRenderedAsTwig(), which gates rendering only on the field definition's allowtwig flag and a regex checking for {{, {%, or {#; when true, the raw field value is compiled and rendered via self::getTwig()->createTemplate($value)->render(['record' => $this->getContent()]) with no sandboxing. Bolt's own bundled config/bolt/contenttypes.yaml sets allowtwig: true on the default "pages" contenttype's content field out of the box. Any user with edit access to that content type (a standard editor role, not just an administrator) can inject a Twig payload such as {{ ['id']|map('passthru')|join }} that executes arbitrary OS commands when the content is saved and rendered, achieving remote code execution as the web server user.