CVE-2025-66301: Getgrav Grav Auth Bypass Vulnerability

CVE-2025-66301 Overview

CVE-2025-66301 is a high-severity authorization bypass vulnerability affecting Grav, a popular file-based Web platform. The vulnerability exists in the admin panel's page editing functionality, where improper authorization checks allow editors with limited permissions to modify critical form configuration fields. An attacker with basic editor access can manipulate the YAML frontmatter through the data[_json][header][form] parameter, potentially altering form processing behavior and enabling further exploitation.

Critical Impact

Low-privileged editors can bypass authorization controls to modify form processing configurations, potentially leading to privilege escalation and additional security compromises through manipulated form actions.

Affected Products

• Grav CMS versions prior to 1.8.0-beta.27
• Grav CMS 1.8.0-beta.1 through 1.8.0-beta.26
• All Grav installations using the admin panel with multi-user editor access

Discovery Timeline

• 2025-12-01 - CVE-2025-66301 published to NVD
• 2025-12-03 - Last updated in NVD database

Technical Details for CVE-2025-66301

Vulnerability Analysis

This vulnerability is classified as CWE-285 (Improper Authorization) and carries a CVSS 4.0 score of 8.6 (HIGH). The CVSS vector CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X indicates network-accessible exploitation with low attack complexity, requiring only low privileges and no user interaction.

The Exploit Prediction Scoring System (EPSS) rates this vulnerability at 32.399% probability of exploitation, placing it in the 96.674th percentile—indicating a significantly elevated risk of real-world exploitation compared to other vulnerabilities.

Root Cause

The root cause stems from insufficient authorization validation when processing POST requests to the /admin/pages/{page_name} endpoint. The application fails to properly verify whether the authenticated user has the necessary permissions to modify the data[_json][header][form] field, which contains the YAML frontmatter configuration. This frontmatter includes the critical process section that defines post-submission actions for forms.

Grav's architecture allows page content to be stored with associated metadata in YAML format at the top of page files. When an editor submits changes, the backend processes all submitted form fields without adequately checking if the user's role permits modification of form processing directives.

Attack Vector

The attack vector is network-based and requires authenticated access with at least editor-level privileges. An attacker can exploit this vulnerability through the following mechanism:

1. An attacker authenticates to the Grav admin panel with editor credentials that have limited permissions (only basic content editing)
2. The attacker navigates to edit a page containing a form definition
3. By intercepting or crafting a POST request to /admin/pages/{page_name}, the attacker includes modified values in the data[_json][header][form] parameter
4. The modified YAML frontmatter can alter the process section to execute unintended actions when users submit the form
5. Since authorization checks are insufficient, the malicious modifications are saved and take effect

The vulnerability allows manipulation of form processing directives which can include email notifications, file operations, and other sensitive actions—potentially enabling data exfiltration, spam distribution, or chaining with other vulnerabilities for further system compromise.

For detailed technical information and proof-of-concept details, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-66301

Indicators of Compromise

• Unexpected modifications to page YAML frontmatter, particularly in the form and process sections
• Audit logs showing POST requests to /admin/pages/* endpoints from users with limited editor roles
• Changes to form processing configurations that don't align with legitimate administrative activities

Detection Strategies

Organizations can implement detection through several approaches:

Log Analysis: Monitor Grav admin panel access logs for POST requests to /admin/pages/{page_name} endpoints. Flag requests that contain data[_json][header][form] parameters from users who should only have basic content editing permissions.

File Integrity Monitoring: Implement monitoring on Grav page files (typically stored in user/pages/) to detect unauthorized changes to YAML frontmatter sections, particularly modifications to form: and process: blocks.

User Activity Auditing: Review user activity within the Grav admin panel, looking for editors accessing or modifying pages beyond their assigned scope, especially those containing form definitions.

Monitoring Recommendations

Deploy web application firewall (WAF) rules to inspect POST request bodies for attempts to modify protected form fields. Configure alerting for any changes to form processing configurations outside of approved change windows. Regularly audit user permissions within Grav to ensure the principle of least privilege is enforced, and consider implementing additional logging for all administrative actions affecting page metadata.

How to Mitigate CVE-2025-66301

Immediate Actions Required

• Upgrade Grav CMS to version 1.8.0-beta.27 or later immediately
• Audit all existing page forms for unauthorized modifications to the process section
• Review editor account permissions and restrict access to only necessary functionality
• Temporarily disable editor access to pages containing sensitive forms until patched

Patch Information

The vulnerability is fixed in Grav version 1.8.0-beta.27. Organizations should update their Grav installations through the official update mechanism:

1. Back up your Grav installation, including the user/ directory
2. Access the Grav admin panel and navigate to the update section
3. Apply the update to version 1.8.0-beta.27 or later
4. Verify the update was successful and test form functionality
5. Review changelogs for any breaking changes that may affect custom implementations

For installations that cannot use the built-in updater, download the latest release from the official Grav repository and follow manual upgrade procedures.

Workarounds

If immediate patching is not possible, implement the following temporary mitigations:

Restrict Editor Access: Remove editor permissions for accounts that don't require the ability to modify pages. Limit form-containing pages to administrator-only access.

Implement WAF Rules: Deploy web application firewall rules to block or flag POST requests containing data[_json][header][form] parameters from non-administrative users.

File System Permissions: Where feasible, set file system permissions on critical page files to prevent modification by the web server user, though this may impact legitimate admin functionality.

# Example: Restrict write access to sensitive form pages (use with caution)
chmod 444 /path/to/grav/user/pages/sensitive-form/form.md
# Note: This will prevent ALL modifications including legitimate admin changes
# Re-enable with: chmod 644 /path/to/grav/user/pages/sensitive-form/form.md