CVE-2025-49298 is a Stored Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the 'Event post' product developed by Bastien Ho. This vulnerability arises due to improper neutralization of input during web page generation, allowing malicious scripts to be stored and later executed in the context of a victim's browser. The affected versions include all versions up to 5.10.1, with no specific lower bound version identified. The vulnerability has a CVSS 3.1 base score of 6.5, indicating a medium severity level. The CVSS vector (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L) reveals that the attack can be executed remotely over the network with low attack complexity, requires low privileges, and user interaction is necessary. The scope is changed, meaning the vulnerability affects resources beyond the initially vulnerable component. The impact affects confidentiality, integrity, and availability at a low level. Stored XSS vulnerabilities allow attackers to inject malicious JavaScript code that is permanently stored on the target server (e.g., in a database) and executed when other users access the affected pages. This can lead to session hijacking, credential theft, defacement, or distribution of malware. Although no known exploits are currently reported in the wild, the presence of stored XSS in a web-facing event posting system poses a significant risk, especially if the platform is widely used for event management or communication. The lack of available patches or mitigation links suggests that users must proactively implement protective measures until an official fix is released.

For European organizations using the Bastien Ho Event post software, this vulnerability could lead to unauthorized access to user sessions, theft of sensitive information, and potential defacement or manipulation of event-related content. Given the nature of event management platforms, attackers could exploit this to spread misinformation, conduct phishing attacks, or compromise user accounts. The confidentiality impact includes potential exposure of user data, while integrity and availability impacts could disrupt event operations or damage organizational reputation. In sectors such as education, government, or large enterprises that rely on event management tools for communication and coordination, the consequences could be more severe. Additionally, GDPR regulations in Europe impose strict requirements on data protection; exploitation of this vulnerability leading to data breaches could result in significant legal and financial penalties.

1. Immediate implementation of input validation and output encoding: Ensure that all user-supplied input is properly sanitized and encoded before rendering in web pages to prevent script injection. 2. Employ Content Security Policy (CSP): Deploy CSP headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. 3. Use HTTP-only and Secure flags on cookies: This limits the ability of malicious scripts to access session cookies. 4. Restrict privileges: Since the vulnerability requires low privileges, minimize user permissions to reduce attack surface. 5. Monitor and audit logs: Regularly review server and application logs for suspicious activity indicative of exploitation attempts. 6. Educate users: Train users to recognize phishing or suspicious links that might exploit XSS. 7. Isolate vulnerable components: If possible, segregate the Event post application from critical systems to limit lateral movement. 8. Stay updated: Monitor vendor announcements for patches or updates and apply them promptly once available. 9. Implement Web Application Firewalls (WAF): Configure WAF rules to detect and block common XSS payloads targeting the Event post application.