CVE-2025-66294 is a Server-Side Template Injection (SSTI) vulnerability found in Grav, a popular file-based web platform used for content management. The vulnerability exists in versions prior to 1.8.0-beta.27 and arises from insufficient input validation in the cleanDangerousTwig method, which uses weak regular expressions to sanitize template code. This flaw allows attackers with editor-level authentication to inject and execute arbitrary code on the server, potentially leading to full system compromise. Under certain conditions, unauthenticated attackers may also exploit this vulnerability, increasing the attack surface. The vulnerability is categorized under CWE-94 (Improper Control of Generation of Code) and CWE-1336 (Weak Regular Expression). The CVSS 4.0 base score is 8.7, reflecting a network attack vector with low complexity, no user interaction, and high impact on confidentiality, integrity, and availability. Although no exploits are currently known in the wild, the vulnerability’s characteristics make it a critical risk for Grav users. The fix was introduced in version 1.8.0-beta.27, which strengthens input validation and sanitization to prevent code injection. Organizations relying on Grav for web content management should prioritize patching to mitigate this risk.

The impact of CVE-2025-66294 on European organizations can be severe. Successful exploitation allows attackers to execute arbitrary commands on the server hosting Grav, potentially leading to data breaches, defacement, or full server takeover. This compromises the confidentiality, integrity, and availability of web services and any sensitive data processed or stored by the platform. For organizations using Grav in critical infrastructure sectors such as government, finance, healthcare, or media, the consequences could include operational disruption, reputational damage, and regulatory penalties under GDPR. The possibility of unauthenticated exploitation under certain conditions increases the risk profile, especially for publicly accessible Grav instances. European companies with multiple editors or contributors on their Grav sites face elevated risk due to the requirement of editor-level permissions for exploitation. The vulnerability also poses a threat to supply chains relying on Grav-based web services. Overall, the threat could facilitate lateral movement within networks and serve as a foothold for broader attacks.

To mitigate CVE-2025-66294, organizations should immediately upgrade all Grav installations to version 1.8.0-beta.27 or later, where the vulnerability is patched. Until upgrades are applied, restrict editor permissions to trusted users only and audit existing editor accounts for suspicious activity. Implement strict input validation and sanitization policies on any user-generated content that interacts with Grav templates. Employ web application firewalls (WAFs) with rules targeting SSTI patterns to detect and block exploitation attempts. Monitor server logs for unusual command execution or template rendering errors. Conduct regular security assessments and penetration tests focusing on template injection vectors. Additionally, isolate Grav servers within segmented network zones to limit potential lateral movement. Educate content editors about security best practices and the risks of injecting untrusted code. Finally, maintain an incident response plan tailored to web platform compromises to enable rapid containment and remediation.