CVE-2025-66294 Overview
CVE-2025-66294 is a high-severity Server-Side Template Injection (SSTI) vulnerability in Grav, a popular open-source file-based Web platform. This vulnerability allows authenticated attackers with editor permissions to execute arbitrary commands on the server. Under certain conditions, it may also be exploited by unauthenticated attackers, significantly increasing the risk profile of affected installations.
The vulnerability stems from weak regex validation in the cleanDangerousTwig method, which fails to properly sanitize user-controlled input before it is processed by the Twig templating engine. With a CVSS score of 8.7 and an EPSS probability of 47.06% (97th percentile), this vulnerability presents a significant risk to organizations running vulnerable versions of Grav CMS.
Critical Impact
Attackers can achieve remote code execution on vulnerable Grav installations, potentially leading to complete server compromise, data exfiltration, and lateral movement within the network.
Affected Products
- Grav CMS versions prior to 1.8.0-beta.27
- Grav CMS 1.8.0-beta1 through 1.8.0-beta26
- All stable Grav releases prior to the patched version
Discovery Timeline
- December 1, 2025 - CVE-2025-66294 published to NVD
- December 4, 2025 - Last updated in NVD database
Technical Details for CVE-2025-66294
Vulnerability Analysis
This Server-Side Template Injection vulnerability (CWE-94: Improper Control of Generation of Code) exists within Grav's Twig template processing functionality. Grav utilizes the Twig templating engine to render dynamic content, and the platform implements a cleanDangerousTwig method intended to sanitize potentially dangerous template directives before execution.
The vulnerability carries a CVSS 4.0 vector of CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N, indicating:
- Network-based attack vector - Exploitable remotely over the network
- Low attack complexity - No specialized conditions required
- Low privileges required - Authenticated users with editor permissions can exploit this
- No user interaction needed - Exploitation can occur without victim involvement
- High impact on confidentiality, integrity, and availability - Complete system compromise possible
Root Cause
The root cause of CVE-2025-66294 lies in the insufficient regex-based validation implemented within the cleanDangerousTwig method. This method was designed to filter out potentially dangerous Twig template constructs before they are processed by the templating engine. However, the regex patterns used for validation are too permissive, allowing attackers to craft payloads that bypass the sanitization logic.
Template injection vulnerabilities occur when user input is embedded into template strings that are subsequently evaluated by the template engine. In Twig, attackers can leverage various built-in functions and filters to execute arbitrary PHP code on the server. The weak regex validation fails to account for all possible encoding variations, whitespace manipulation, and alternative syntax constructs that can be used to bypass the filter.
Attack Vector
The attack vector for CVE-2025-66294 is network-based and requires the attacker to have authenticated access with editor permissions in the Grav admin panel. Once authenticated, the attacker can inject malicious Twig template code through content editing interfaces.
The exploitation flow involves:
- Attacker authenticates to the Grav admin panel with editor-level privileges
- Attacker crafts a malicious Twig template payload designed to bypass the cleanDangerousTwig regex validation
- The malicious payload is submitted through a content editing interface
- The Twig engine processes the unsanitized payload, executing arbitrary code on the server
- The attacker gains command execution capabilities on the underlying server
Under certain conditions, unauthenticated attackers may also exploit this vulnerability, potentially through cached content or misconfigured access controls. See the security advisory at https://github.com/getgrav/grav/security/advisories/GHSA-662m-56v4-3r8f for detailed technical information on exploitation methods.
Detection Methods for CVE-2025-66294
Indicators of Compromise
- Unusual Twig template syntax in page content or configuration files
- Unexpected PHP function calls in server access logs
- Anomalous process spawning from web server processes (e.g., php-fpm, apache2, nginx)
- New files created in web directories with suspicious content
- Outbound network connections from web server to unusual destinations
Detection Strategies
Organizations should implement multi-layered detection strategies to identify potential exploitation attempts:
Web Application Firewall (WAF) Rules: Configure WAF rules to detect and block common SSTI payloads targeting Twig templating engine. Look for patterns containing Twig delimiters ({{, }}, {%, %}) combined with dangerous functions like system, exec, passthru, or filter constructs.
Log Analysis: Monitor web application logs for requests containing encoded or obfuscated Twig syntax. Pay particular attention to POST requests to admin panel endpoints that handle content editing.
File Integrity Monitoring: Implement file integrity monitoring on Grav installation directories to detect unauthorized modifications to template files or the creation of new executable content.
Behavioral Analysis: Monitor for anomalous behavior patterns such as web server processes executing system commands, spawning child processes, or establishing outbound network connections.
Monitoring Recommendations
Security teams should implement continuous monitoring for the following:
- Admin Panel Activity: Log and alert on content modifications made through the Grav admin panel, particularly those containing template syntax
- Process Monitoring: Use endpoint detection and response (EDR) solutions to monitor for suspicious process chains originating from web server processes
- Network Traffic Analysis: Monitor for command-and-control traffic patterns and data exfiltration attempts from web servers
- Version Tracking: Maintain an inventory of Grav installations and their versions to quickly identify vulnerable systems
How to Mitigate CVE-2025-66294
Immediate Actions Required
- Upgrade Grav CMS to version 1.8.0-beta.27 or later immediately
- Review admin panel access logs for suspicious activity
- Audit user accounts with editor or higher permissions
- Implement Web Application Firewall (WAF) rules to block SSTI payloads
- Enable enhanced logging on Grav installations pending upgrade
Patch Information
The vulnerability is addressed in Grav version 1.8.0-beta.27. The security patch improves the regex validation in the cleanDangerousTwig method to properly sanitize dangerous Twig template constructs.
Patch Commit: The fix is available in commit e37259527d9c1deb6200f8967197a9fa587c6458
Patch URL: https://github.com/getgrav/grav/commit/e37259527d9c1deb6200f8967197a9fa587c6458
Organizations should prioritize upgrading to the patched version. Review the vendor security advisory at https://github.com/getgrav/grav/security/advisories/GHSA-662m-56v4-3r8f for complete upgrade instructions and additional security recommendations.
Workarounds
If immediate patching is not possible, organizations should implement the following temporary mitigations:
Restrict Admin Access: Limit access to the Grav admin panel by IP address using web server configuration or firewall rules. Only allow trusted administrative IP addresses to access the /admin endpoint.
Review User Permissions: Audit all user accounts with editor permissions and remove access from any accounts that do not require content editing capabilities.
Enable Two-Factor Authentication: If available, enable two-factor authentication for all admin panel accounts to reduce the risk of unauthorized access.
Deploy WAF Protection: Implement Web Application Firewall rules specifically designed to detect and block Server-Side Template Injection payloads targeting Twig.
# Example: Restrict admin access by IP in Apache .htaccess
<Location /admin>
Require ip 192.168.1.0/24
Require ip 10.0.0.0/8
</Location>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
