CVE-2025-11570 identifies a Cross-site Scripting (XSS) vulnerability in the drupal-pattern-lab/unified-twig-extensions package, specifically version 0.0.0. The root cause is insufficient filtering of user-supplied data before rendering in Twig templates, which can lead to injection and execution of arbitrary JavaScript code in the victim's browser. This vulnerability is exploitable only when the vulnerable code is executed outside the Drupal CMS environment, as the function is intended to be shared between Drupal and Pattern Lab, a tool used for UI pattern development. The package itself is unmaintained, meaning no direct fixes will be issued for it; however, the maintained drupal/unified_twig_ext package version 1.1.1 contains a fix addressing this issue. The CVSS 4.0 vector indicates the attack can be performed remotely over the network without privileges but requires user interaction, such as clicking a malicious link or visiting a crafted page. The impact on confidentiality and integrity is low, as the vulnerability primarily enables script execution in the context of the affected web application, potentially leading to session hijacking or UI manipulation. Availability is not impacted. No known exploits have been observed in the wild, suggesting limited active exploitation at this time. The vulnerability highlights the risks of using unmaintained third-party packages and the importance of applying security patches or migrating to maintained alternatives.

For European organizations, the primary impact is the risk of client-side script injection leading to session hijacking, credential theft, or unauthorized actions performed in the context of authenticated users. Organizations using the vulnerable package outside of Drupal—particularly in Pattern Lab workflows or custom integrations—may expose their users to malicious payloads. This could damage user trust, lead to data leakage, or facilitate further attacks such as phishing or privilege escalation. Since the vulnerability requires user interaction and is limited to non-Drupal contexts, the attack surface is somewhat constrained. However, organizations with public-facing development or design environments using Pattern Lab could be targeted. The medium severity rating indicates a moderate risk that should be addressed promptly to avoid exploitation. The lack of known exploits reduces immediate urgency but does not eliminate the threat. Compliance with European data protection regulations (e.g., GDPR) may also be impacted if user data is compromised through this vulnerability.

European organizations should take the following specific steps: 1) Identify all instances where drupal-pattern-lab/unified-twig-extensions version 0.0.0 is used, especially outside Drupal environments. 2) Migrate to the maintained drupal/unified_twig_ext package version 1.1.1, which contains the fix for this vulnerability. 3) If migration is not immediately possible, implement strict input validation and output encoding in Twig templates to sanitize user-supplied data and prevent script injection. 4) Restrict access to Pattern Lab environments and ensure they are not publicly exposed or accessible without authentication. 5) Monitor web application logs and user reports for suspicious activity indicative of XSS exploitation attempts. 6) Educate developers and content creators on the risks of using unmaintained packages and the importance of applying security updates. 7) Incorporate automated dependency scanning tools in CI/CD pipelines to detect vulnerable packages early. 8) Review and harden Content Security Policy (CSP) headers to limit the impact of potential XSS attacks. These targeted actions go beyond generic advice by focusing on the specific package, usage context, and environment exposure.