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The vulnerability CVE-2025-66301 in Grav is an authorization bypass that allows a user with basic page editing permissions to escalate privileges by modifying the underlying form definition. It works by exploiting improper authorization checks on the POST request endpoint /admin/pages/{page_name}. An authenticated editor, who should only be able to modify basic page content, can instead send a crafted request containing a modified `data[bash][header][bash]` field. This field contains the YAML frontmatter that defines the form’s `process` section, which controls backend actions executed upon form submission. By injecting custom YAML processes, the attacker can reconfigure the form to perform unauthorized actions, such as executing arbitrary PHP code, creating administrative users, or writing malicious files to the server, leading to remote code execution and full system compromise.
Platform: Grav CMS
Version: <1.8.0-beta.27
Vulnerability: YAML Injection
Severity: Critical
date: 12/01/2025
Prediction: 12/10/2025
What Undercode Say:
curl -X POST ‘https://target/admin/pages/test’ -H ‘Authorization: Bearer TOKEN’ –data ‘data[bash][header][bash]=…’
process:
- exec: ‘php -r evil_code’
grep -r “form:” /user/pages/
find . -name “.yaml” -exec grep -l “process:” {} \;
How Exploit:
1. Attacker logs in with editor account.
2. Navigates to page edit form.
3. Intercepts POST request to `/admin/pages/page_name`.
- Modifies `data[bash][header][bash]` parameter with malicious YAML `process` directives.
- Submits the request, injecting new backend form behavior.
- The new process executes upon the next legitimate form submission, granting attacker higher privileges or RCE.
Protection from this CVE:
Update to version 1.8.0-beta.27.
Implement proper authorization checks.
Sanitize user-controlled YAML input.
Apply role-based access controls.
Impact:
Privilege Escalation
Remote Code Execution
Total System Compromise
Data Breach
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Sources:
Reported By: nvd.nist.gov
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