CVE-2025-66301 is an improper authorization vulnerability classified under CWE-285, discovered in the Grav CMS platform before version 1.8.0-beta.27. Grav is a flat-file CMS that uses YAML frontmatter to configure page metadata and form processing logic. The vulnerability arises because the platform fails to properly enforce authorization checks when an editor submits a POST request to modify pages via the /admin/pages/{page_name} endpoint. Specifically, editors with permissions limited to basic content changes can manipulate the data[_json][header][form] field, which contains YAML frontmatter including the 'process' section. This section controls post-submission form actions such as email notifications, redirects, or other workflows. By altering this, an attacker can change the form's behavior, potentially enabling unauthorized actions or chaining further exploits. The vulnerability does not require elevated privileges beyond editor-level access, no user interaction, and can be exploited remotely over the network. 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 high impact on confidentiality and integrity. No known exploits are reported in the wild as of publication. The issue was addressed in Grav 1.8.0-beta.27 by enforcing stricter authorization checks on modifications to critical YAML frontmatter fields.

For European organizations, this vulnerability poses a significant risk especially to those using Grav CMS for public-facing websites or internal portals with editor-level users. Exploitation can lead to unauthorized modification of form processing logic, potentially allowing attackers to intercept or redirect form submissions, execute unauthorized workflows, or facilitate further attacks such as phishing or data exfiltration. The impact on confidentiality and integrity is high, as sensitive data submitted via forms could be compromised or manipulated. Availability impact is less direct but could occur if form processing is disrupted. Organizations in sectors with strict data protection regulations (e.g., GDPR) face compliance risks if personal data is exposed or mishandled. The vulnerability's ease of exploitation and lack of user interaction requirement increase the threat level. Given Grav's popularity in European small and medium enterprises and web agencies, the risk is non-trivial.

1. Upgrade all Grav installations to version 1.8.0-beta.27 or later immediately to apply the official fix. 2. Review and restrict editor permissions to the minimum necessary, avoiding granting access to modify form-related YAML frontmatter unless absolutely required. 3. Implement strict input validation and sanitization on form data and YAML frontmatter fields where possible. 4. Monitor administrative logs for unusual POST requests to /admin/pages/{page_name} that attempt to modify the data[_json][header][form] field. 5. Employ web application firewalls (WAFs) with custom rules to detect and block suspicious modifications to form processing data. 6. Conduct regular security audits and penetration testing focusing on CMS administrative interfaces. 7. Educate content editors about the risks of unauthorized changes and enforce strong authentication and session management controls to prevent account compromise.