Executive brief
Microweber CMS, a website builder and content management system, contains a security flaw in how it handles email templates. An administrator can insert malicious code into these templates that allows them to take full control of the underlying web server. Once the code is saved, it will automatically run whenever the system sends an email, such as during a new order or user registration, potentially leading to data theft or a complete service shutdown.
Technical details
Microweber CMS through 2.0.20 is vulnerable to Server-Side Template Injection (SSTI) leading to Remote Code Execution (RCE). The vulnerability exists in the TwigView::render() method and other inline Twig environments which fail to implement Twig's SandboxExtension or a SecurityPolicy. An authenticated administrator can inject malicious Twig expressions, such as filter('system'), into mail template bodies. These templates are stored unsanitized in the database and executed whenever a system event (like a checkout or registration) triggers a mail dispatch. As the project is reportedly abandoned, no official patch is available; users are advised to manually implement a strict Twig security policy or restrict access to the template editor.
Affected products
- Microweber Microweber CMS <= 2.0.20
Timeline
- 2026-07-15: disclosed: Vulnerability discovered and reported to VulnCheck
- 2026-07-23: advisory: Public disclosure via GitHub Gist
- 2026-07-24: other: CVE published to NVD dataset