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The CVE-2025-66294 vulnerability in Grav arises from inadequate regex validation in the cleanDangerousTwig method, which is intended to sanitize Twig templates to prevent Server-Side Template Injection (SSTI). This method uses weak regular expressions that fail to properly filter dangerous Twig functions or tags, allowing attackers to bypass sanitization. Authenticated users with editor permissions can inject malicious Twig templates through template editing features, such as in the admin panel. The injected templates are then rendered by the Twig engine on the server, executing arbitrary code. This can include system commands or PHP code, leading to remote code execution. Under certain conditions, like misconfigurations that expose template editing without authentication, unauthenticated attackers may also exploit this. The vulnerability leverages obfuscated function names, alternative syntax, or encoding to evade regex detection. Once exploited, attackers gain shell access, can read sensitive files, modify data, or compromise the entire server. The weak regex likely misses patterns like {{ system(‘command’) }} or similar payloads, enabling full server control. This SSTI flaw highlights the risks of insufficient input validation in template engines, especially in file-based CMS platforms like Grav.
Platform: Grav
Version: Prior to 1.8.0-beta.27
Vulnerability: Server-Side Template Injection
Severity: Critical
date: 12/01/2025
Prediction: Patched in 1.8.0-beta.27
What Undercode Say:
Analytics:
Check Grav version for vulnerability
find /path/to/grav -name "system.yaml" -exec grep "version" {} \;
Locate cleanDangerousTwig method in source
grep -r "cleanDangerousTwig" /var/www/html/grav/
Test endpoint for SSTI with curl (educational)
curl -X POST http://target.com/admin -d "template={{77}}"
How Exploit:
Authenticated attackers inject Twig code via template editing, exploiting weak regex to execute commands. Unauthenticated exploitation may involve crafted requests to vulnerable endpoints.
Protection from this CVE:
Upgrade to Grav 1.8.0-beta.27 or later. Restrict editor permissions. Use WAF rules.
Impact:
Remote Code Execution, server compromise, data breach.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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