CVE-2025-66301 is an improper authorization vulnerability classified under CWE-285 affecting Grav, a popular file-based web platform used for content management. The flaw exists in versions prior to 1.8.0-beta.27, where the authorization checks on POST requests to the endpoint /admin/pages/{page_name} are insufficient. Specifically, an editor with permissions limited to basic content changes can manipulate the data[_json][header][form] field, which contains the YAML frontmatter of a page. This YAML frontmatter includes a 'process' section that controls the form's behavior after submission, such as triggering actions or workflows. By altering this section, an attacker can change the form's processing logic, potentially enabling unauthorized actions or chaining further vulnerabilities. The vulnerability does not require user interaction or elevated privileges beyond editor access, making it easier to exploit within compromised or insider accounts. The CVSS 4.0 vector (AV:N/AC:L/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N) reflects a network attack vector with low complexity, requiring limited privileges but no user interaction, and causing high confidentiality and integrity impacts without affecting availability. No known exploits are currently reported in the wild. The issue was publicly disclosed on December 1, 2025, and fixed in Grav version 1.8.0-beta.27.

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of web content and form processing workflows managed via Grav. Attackers or malicious insiders with editor-level access can manipulate form behaviors, potentially injecting malicious processing steps or bypassing intended workflows. This could lead to unauthorized data exposure, privilege escalation, or further exploitation of backend systems. Organizations using Grav for critical web services, customer-facing forms, or internal portals may face data breaches or service manipulation. The vulnerability's ease of exploitation and lack of user interaction requirement increase the threat level. Given Grav's usage in various European countries for lightweight CMS solutions, the impact could extend to government, education, and small to medium enterprises relying on this platform for web content management.

The primary mitigation is to upgrade all Grav installations to version 1.8.0-beta.27 or later, where the authorization checks have been corrected. Until upgrades can be applied, organizations should restrict editor permissions to prevent access to the YAML frontmatter fields, especially the data[_json][header][form] section. Implement strict role-based access controls (RBAC) to limit who can modify form processing configurations. Additionally, monitor and audit changes to page configurations and form processing logic for unauthorized modifications. Employ web application firewalls (WAFs) to detect and block suspicious POST requests targeting /admin/pages/{page_name}. Regularly review and harden CMS configurations and ensure that editors are trained on security best practices. Finally, maintain an incident response plan to quickly address any detected exploitation attempts.