CVE-2026-71291 in core
Summary
by MITRE • 08/05/2026
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 allow_twig 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 `allow_twig: 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.
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Analysis
by VulDB Data Team • 08/05/2026
This vulnerability represents a critical server-side template injection flaw in Bolt CMS that stems from improper trust boundaries between user input and the Twig templating engine. The core issue lies in the getTwigValue() method within src/Entity/Field.php which directly processes user-supplied content without adequate sandboxing mechanisms. When a field definition includes allow_twig: true and contains Twig syntax markers such as {{, {%, or {#, the system automatically compiles and executes the raw content through Twig's full application-level environment. This design pattern violates fundamental security principles by granting unrestricted template execution privileges to users who should only have basic content editing capabilities.
The vulnerability operates through a well-defined attack chain that begins with user privilege escalation from standard editor roles to full system compromise. The default configuration in config/bolt/contenttypes.yaml explicitly enables Twig processing for the pages content type's content field, creating an inherent trust model that assumes all content within this field is safe. However, this assumption fails spectacularly when malicious users leverage the allow_twig flag combined with legitimate Twig syntax to inject command execution payloads such as {{ ['id']|map('passthru')|join }}. This particular payload exploits Twig's filter system to execute operating system commands through the passthru function, effectively bypassing traditional input validation mechanisms.
The operational impact of this vulnerability extends far beyond simple data manipulation, reaching into full system compromise and persistent access capabilities. An authenticated user with edit permissions to the pages content type can execute arbitrary operating system commands with the privileges of the web server process, typically running as a dedicated user account such as www-data or IIS_IUSRS. This privilege escalation enables attackers to exfiltrate sensitive data, install backdoors, deploy additional malware, or pivot to compromise other systems within the network infrastructure. The vulnerability exists at the application layer and affects all versions of Bolt CMS that have not implemented proper sandboxing measures, making it particularly dangerous in multi-tenant hosting environments where multiple sites share the same underlying software stack.
Security mitigations for this vulnerability should focus on implementing robust template sandboxing mechanisms that align with industry standards such as CWE-74 and CWE-94. The recommended approach involves configuring Twig's sandbox extension to restrict access to dangerous functions, filters, and methods that could enable command execution or file system manipulation. Organizations should disable allow_twig functionality for user-editable fields unless absolutely necessary, implement strict input validation and sanitization for all content fields, and consider adopting the ATT&CK framework's T1059.001 technique detection patterns to monitor for suspicious template execution patterns. Additionally, comprehensive logging of template compilation events and user access patterns should be implemented to provide visibility into potential exploitation attempts. The most effective long-term solution requires implementing a principle of least privilege model where even privileged users cannot bypass the security controls that protect against server-side template injection attacks.