CVE-2025-39509 is a Stored Cross-Site Scripting (XSS) vulnerability identified in ThemeNcode's TNC FlipBook product, affecting versions up to and including 12.1.0. This vulnerability arises from improper neutralization of input during web page generation, classified under CWE-79. Stored XSS occurs when malicious input is saved by the application and later rendered in web pages without proper sanitization or encoding, allowing attackers to inject and execute arbitrary JavaScript code in the context of users' browsers. The CVSS 3.1 base score for this vulnerability is 6.5, indicating a medium severity level. The vector string (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 (authenticated user), and user interaction is necessary. The scope is changed, meaning the vulnerability affects resources beyond the initially vulnerable component. The impact includes limited confidentiality, integrity, and availability losses, as the injected script can steal session tokens, manipulate page content, or perform actions on behalf of the user. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability was reserved in April 2025 and published in May 2025. Given that TNC FlipBook is a web-based digital flipbook solution used to create interactive publications, the vulnerability could be exploited by authenticated users or attackers who can submit content to the system, potentially affecting administrators or end-users who view the compromised content.

For European organizations using TNC FlipBook, this vulnerability poses a risk of session hijacking, unauthorized actions, and data theft through malicious script execution in users' browsers. Organizations in sectors such as publishing, education, marketing, and corporate communications that rely on interactive digital publications could see reputational damage and potential data breaches if attackers exploit this flaw. The medium severity score reflects that while the vulnerability requires some level of authentication and user interaction, the potential for cross-site scripting to escalate privileges or pivot to further attacks remains significant. Additionally, the scope change indicates that the impact could extend beyond the immediate component, possibly affecting other integrated systems or user sessions. Given the lack of known exploits, the threat is currently theoretical but should be addressed proactively to prevent exploitation, especially in environments with sensitive or regulated data.

1. Apply patches or updates from ThemeNcode as soon as they become available to address this vulnerability. 2. In the absence of patches, implement strict input validation and output encoding on all user-supplied content within TNC FlipBook, especially for fields that are stored and later rendered. 3. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 4. Limit user privileges to the minimum necessary, reducing the risk posed by low-privilege authenticated users. 5. Conduct regular security audits and penetration testing focusing on web application input handling and stored content. 6. Educate users and administrators about the risks of clicking on suspicious links or interacting with untrusted content within the flipbooks. 7. Monitor logs and user activity for unusual behavior that could indicate exploitation attempts. 8. Consider deploying Web Application Firewalls (WAF) with rules tailored to detect and block XSS payloads targeting TNC FlipBook.