CVE-2025-39463 is a critical security vulnerability categorized as Remote File Inclusion (RFI) found in the Select-Themes Dessau PHP program, affecting all versions prior to 1.9. The root cause is improper control over the filename parameter used in PHP's include or require statements, which allows an attacker to specify a remote file to be included and executed by the server. This flaw enables unauthenticated remote attackers to execute arbitrary PHP code, potentially leading to full system compromise, data theft, or denial of service. The vulnerability has a CVSS v3.1 base score of 9.8, reflecting its critical nature with network attack vector, no required privileges or user interaction, and full impact on confidentiality, integrity, and availability. Although no public exploits have been reported yet, the vulnerability's characteristics make it highly exploitable. The affected product, Dessau, is a PHP theme commonly used in web applications, and the flaw stems from insufficient input validation and lack of secure coding practices around file inclusion mechanisms. The vulnerability was reserved in April 2025 and published in November 2025, indicating recent discovery and disclosure. The absence of official patches at the time of reporting increases the urgency for organizations to implement interim mitigations and monitor for updates from Select-Themes.

For European organizations, this vulnerability poses a severe risk due to the widespread use of PHP-based web applications and CMS platforms that may incorporate the Dessau theme. Exploitation can lead to unauthorized remote code execution, allowing attackers to gain control over web servers, access sensitive customer and business data, deface websites, or disrupt services. This can result in significant financial losses, reputational damage, and regulatory penalties under GDPR for data breaches. The critical nature of the vulnerability means that even organizations with limited security controls are at risk, and automated exploitation attempts may increase rapidly once public exploits emerge. Sectors such as e-commerce, government portals, and media companies that rely on PHP themes for their web presence are particularly vulnerable. The impact extends beyond the initial compromise, as attackers may use the foothold to pivot into internal networks or deploy ransomware. Given the high CVSS score and no authentication required, the threat is immediate and severe for European entities using affected versions.

1. Immediately inventory all web applications and servers using the Select-Themes Dessau theme and identify versions prior to 1.9. 2. Apply official patches or updates from Select-Themes as soon as they become available. 3. Until patches are released, implement strict input validation and sanitization on all parameters that influence file inclusion paths to prevent injection of remote URLs. 4. Disable allow_url_include and allow_url_fopen directives in PHP configurations to prevent remote file inclusion. 5. Employ Web Application Firewalls (WAFs) with rules designed to detect and block suspicious file inclusion attempts. 6. Conduct regular vulnerability scanning and penetration testing focused on file inclusion vulnerabilities. 7. Monitor web server logs for unusual requests that attempt to include remote files or access unexpected URLs. 8. Educate development teams on secure coding practices to avoid dynamic file inclusion without proper validation. 9. Isolate web servers hosting vulnerable applications to limit lateral movement in case of compromise. 10. Prepare incident response plans to quickly address potential exploitation events.