CVE-2024-56156 is a vulnerability identified in the open source website building tool Halo, specifically in versions prior to 2.20.13. The root cause is an improper neutralization of input during web page generation, classified under CWE-79 (Cross-site Scripting). The vulnerability allows attackers to bypass file type validation controls intended to restrict uploads to safe file types. By exploiting this bypass, attackers can upload malicious files, including executable binaries and HTML files containing malicious scripts. These files can be stored on the server and later executed in the context of users visiting the affected website, resulting in stored XSS attacks. Stored XSS can lead to session hijacking, data theft, or further exploitation of the server environment. In some scenarios, this vulnerability can escalate to remote code execution, allowing attackers to execute arbitrary code on the server hosting Halo. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. The CVSS v4.0 score is 5.5 (medium severity), reflecting the moderate impact and ease of exploitation. The vulnerability has been patched in Halo version 2.20.13, and no known active exploits have been reported. Organizations running vulnerable versions should prioritize patching and review their file upload handling and input sanitization mechanisms to prevent exploitation.

For European organizations, the impact of CVE-2024-56156 can be significant, particularly for those relying on Halo for public-facing websites or internal portals. Successful exploitation can lead to stored XSS attacks, compromising user sessions, stealing sensitive data, or defacing websites, which can damage reputation and trust. In worst-case scenarios, remote code execution could allow attackers to gain control over the web server, leading to data breaches, lateral movement within networks, or deployment of ransomware. This risk is heightened in sectors with strict data protection regulations such as GDPR, where data breaches can result in heavy fines and legal consequences. Additionally, organizations in critical infrastructure, government, and finance sectors are at increased risk due to the potential for disruption and espionage. The vulnerability’s ease of exploitation without authentication means that attackers can target vulnerable systems at scale, increasing the threat landscape for European entities using this software.

1. Immediately upgrade all instances of Halo to version 2.20.13 or later to apply the official patch addressing this vulnerability. 2. Implement strict server-side validation of file uploads, ensuring only allowed file types are accepted and scanned for malicious content. 3. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 4. Regularly audit and sanitize all user inputs and outputs, especially those involved in file uploads and web page generation. 5. Monitor web server logs for unusual upload activity or access patterns that may indicate exploitation attempts. 6. Conduct penetration testing focused on file upload mechanisms and XSS vulnerabilities to identify residual risks. 7. Educate developers and administrators on secure coding practices related to input validation and output encoding. 8. Consider deploying Web Application Firewalls (WAFs) with rules tuned to detect and block XSS payloads and suspicious file uploads. 9. Maintain an incident response plan to quickly address any exploitation attempts or breaches related to this vulnerability.