CVE-2025-66298 Overview
CVE-2025-66298 is a high-severity Server-Side Template Injection (SSTI) vulnerability in Grav CMS, a popular file-based web platform. This vulnerability allows attackers to exploit form handling functionality to expose sensitive configuration details, including the complete Grav configuration and plugin settings, through specially crafted POST payloads.
Critical Impact
Attackers can extract sensitive configuration information including database credentials, API keys, and plugin secrets by exploiting SSTI in sites with basic form functionality enabled.
Affected Products
- Grav CMS versions prior to 1.8.0-beta.27
- Grav CMS 1.8.0-beta1 through 1.8.0-beta26
- Any Grav installation with form functionality enabled
Discovery Timeline
- December 1, 2025 - CVE-2025-66298 published to NVD
- December 3, 2025 - Last updated in NVD database
Technical Details for CVE-2025-66298
Vulnerability Analysis
This Server-Side Template Injection vulnerability exists in Grav CMS's form processing mechanism. The vulnerability is classified under CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine). With a CVSS 4.0 score of 7.7 (HIGH), the vulnerability presents significant risk due to its network-accessible attack vector requiring no authentication or user interaction.
The CVSS vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/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/SA:X/AU:X/R:X/V:X/RE:X/U:X indicates high confidentiality impact with no integrity or availability impact, meaning attackers can read sensitive data but cannot modify or disrupt services.
The current EPSS score is 0.04% (12th percentile), indicating relatively low predicted exploitation probability at this time.
Root Cause
The root cause lies in improper sanitization of user-supplied input within Grav's template engine. When processing form submissions, the application fails to adequately neutralize special elements that can be interpreted as template directives. This allows template expressions embedded in POST data to be evaluated by the Twig template engine, resulting in information disclosure.
Grav uses Twig as its templating engine, and when user input is passed unsanitized into template rendering contexts, attackers can inject Twig syntax to access internal variables including the global configuration object.
Attack Vector
The attack exploits the form handling mechanism present in Grav CMS installations. An attacker needs only to identify a site running a vulnerable version of Grav with any form functionality enabled. By crafting a malicious POST request containing template injection payloads, the attacker can force the server to evaluate template expressions that expose internal configuration data.
The vulnerability can be exploited through:
- Identifying a target Grav CMS installation with form functionality
- Crafting POST requests with template injection payloads targeting configuration objects
- Analyzing server responses to extract sensitive configuration details including API keys, credentials, and plugin secrets
The attack is particularly dangerous because it requires no authentication (PR:N) and no user interaction (UI:N), making it exploitable through automated scanning and exploitation tools. For detailed technical information and proof-of-concept details, see the security advisory on GitHub.
Detection Methods for CVE-2025-66298
Indicators of Compromise
- Unusual POST requests to form endpoints containing Twig template syntax (e.g., {{, {%, }})
- Web server logs showing requests with encoded template expressions in form parameters
- Anomalous access patterns targeting form submission endpoints
- POST requests containing configuration-related template variables like config, system, or grav
Detection Strategies
Organizations can detect exploitation attempts through:
Web Application Firewall (WAF) Rules: Configure WAF rules to detect and block requests containing common SSTI patterns including double curly braces {{, template block indicators {%, and Twig-specific functions like dump(), include(), or access to the _self variable.
Log Analysis: Monitor web server access logs for POST requests to form endpoints that contain template-like syntax patterns. Pay particular attention to URL-encoded variants of template delimiters.
Behavioral Analysis: Implement anomaly detection to identify unusual patterns in form submission data, particularly submissions that deviate significantly from expected input formats.
Monitoring Recommendations
Security teams should implement continuous monitoring for:
- All POST requests to Grav form endpoints
- Error logs indicating template parsing failures or unexpected variable access
- Network traffic analysis for data exfiltration patterns following form submissions
- File integrity monitoring on Grav configuration files to detect unauthorized access attempts
SentinelOne Singularity Platform can provide real-time visibility into web application behavior, detecting anomalous request patterns and potential template injection attempts through its behavioral AI engine.
How to Mitigate CVE-2025-66298
Immediate Actions Required
- Upgrade Grav CMS to version 1.8.0-beta.27 or later immediately
- Audit all form configurations for proper input validation
- Review web server logs for signs of previous exploitation attempts
- Implement WAF rules to block template injection patterns as a defense-in-depth measure
- Consider temporarily disabling form functionality on critical systems until patching is complete
Patch Information
The vulnerability has been fixed in Grav CMS version 1.8.0-beta.27. The patch is available via the official GitHub repository:
- Patch Commit:e37259527d9c1deb6200f8967197a9fa587c6458
- Security Advisory:GHSA-8535-hvm8-2hmv
Organizations should prioritize this patch as the vulnerability is network-accessible and requires no authentication for exploitation.
Workarounds
If immediate patching is not possible, consider the following temporary mitigations:
Disable Forms: Temporarily disable form functionality on affected Grav installations until patching can be completed
WAF Protection: Implement strict WAF rules to filter template injection patterns in form submissions
Network Segmentation: Restrict network access to Grav administrative interfaces and form endpoints
Input Validation: Implement server-side input validation to strip or reject form submissions containing template syntax
# Example nginx configuration to block common SSTI patterns
location ~ \.php$ {
# Block requests containing template injection patterns
if ($request_body ~* "(\{\{|\{%|%\}|\}\})") {
return 403;
}
# Continue with normal PHP processing
fastcgi_pass unix:/var/run/php/php-fpm.sock;
include fastcgi_params;
}
Note that workarounds are temporary measures and should not replace proper patching. Organizations should upgrade to 1.8.0-beta.27 or later as soon as possible.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
