CVE-2025-63416 is a stored Cross-Site Scripting (XSS) vulnerability identified in the chat functionality of the SelfBest platform version 2023.3. This vulnerability allows an authenticated attacker with low privileges to inject arbitrary JavaScript code into chat messages that are stored and later rendered in other users' browsers without proper sanitization. When other users, including administrators, view the malicious chat content, the injected script executes in their browser context. This enables the attacker to perform actions such as stealing session cookies, performing actions on behalf of the victim, and accessing sensitive administrative endpoints like /admin/users. The vulnerability effectively allows privilege escalation by leveraging the victim’s higher privileges, leading to full compromise of sensitive user data and administrative functions. The exploit does not require elevated privileges initially but does require the attacker to be authenticated on the platform. No CVSS score has been assigned yet, and no patches or official mitigations have been published at the time of disclosure. The vulnerability highlights insufficient input validation and output encoding in the chat component, a common vector for stored XSS attacks. The lack of user interaction beyond normal chat usage makes exploitation straightforward once authenticated. The vulnerability poses a significant risk to organizations relying on SelfBest for internal communications, especially where sensitive administrative data is accessible through the platform.

For European organizations, this vulnerability can lead to severe confidentiality and integrity breaches. Attackers can escalate privileges from low-level users to administrators, gaining access to sensitive user data and administrative controls. This can result in data exfiltration, unauthorized changes to user accounts, and potential disruption of services. The ability to access the /admin/users endpoint implies exposure of personally identifiable information (PII) and potentially GDPR-protected data, raising compliance and legal risks. Organizations using SelfBest for internal communication or user management are particularly vulnerable, as attackers can leverage the chat feature to compromise high-value targets. The stored nature of the XSS increases the attack surface since malicious scripts persist and affect multiple users over time. The absence of a patch at disclosure time means organizations must act quickly to implement mitigations to prevent exploitation. The impact is heightened in sectors with strict data protection requirements, such as finance, healthcare, and government institutions across Europe.

Immediate mitigation steps include disabling the chat functionality in SelfBest 2023.3 until a vendor patch is available. Organizations should implement strict input validation and output encoding on all user-generated content, especially chat messages, to prevent script injection. Deploying a robust Content Security Policy (CSP) can help restrict the execution of unauthorized scripts. Monitoring and logging chat activity for suspicious inputs can aid in early detection of exploitation attempts. Administrators should review access logs and user activity for signs of compromise, particularly focusing on the /admin/users endpoint access patterns. User education on phishing and social engineering risks related to session hijacking can reduce impact. Organizations should prioritize applying vendor patches once released and consider multi-factor authentication (MFA) to limit the damage from compromised sessions. Regular security assessments and penetration testing of the platform can help identify similar vulnerabilities proactively.