CVE-2025-49912 is a Stored Cross-site Scripting (XSS) vulnerability identified in the Nks Email Subscription Popup plugin, specifically affecting versions up to 1.2.26. The root cause is improper neutralization of user-supplied input during the generation of web pages, which allows malicious scripts to be injected and stored on the server. When other users access the affected pages, these scripts execute in their browsers within the security context of the vulnerable site. Stored XSS is particularly dangerous because the malicious payload persists on the server and can affect multiple users without requiring repeated exploitation. The vulnerability does not require authentication, meaning any unauthenticated attacker can submit crafted input to the subscription popup. Exploitation requires user interaction, such as visiting a compromised page or interacting with the subscription popup. Potential impacts include theft of session cookies, redirection to malicious sites, defacement, or distribution of malware. Currently, there are no known public exploits or patches available, but the vulnerability has been officially published and reserved since June 2025. The plugin is commonly used in websites to manage email subscriptions, making it a relevant target for attackers aiming to compromise user trust and data. The absence of a CVSS score necessitates an independent severity assessment based on the vulnerability's characteristics.

For European organizations, this vulnerability poses a significant risk to web applications that use the Nks Email Subscription Popup plugin. Exploitation could lead to unauthorized access to user accounts, leakage of sensitive information, and damage to brand reputation. Organizations in sectors with high customer interaction, such as e-commerce, media, and online services, are particularly vulnerable. The stored nature of the XSS means that once exploited, multiple users can be affected, amplifying the impact. Additionally, regulatory frameworks like GDPR impose strict requirements on data protection; a successful attack exploiting this vulnerability could lead to compliance violations and financial penalties. The lack of known exploits currently reduces immediate risk but also means organizations should proactively address the vulnerability before it is weaponized. The vulnerability's ease of exploitation without authentication increases the threat level, especially for publicly accessible websites.

1. Monitor for official patches or updates from the Nks plugin vendor and apply them immediately upon release. 2. Implement strict input validation on all user-supplied data, especially in subscription forms, to reject or sanitize potentially malicious content. 3. Employ robust output encoding techniques to neutralize any untrusted data before rendering it in HTML contexts. 4. Deploy Content Security Policy (CSP) headers to restrict execution of unauthorized scripts and reduce the impact of XSS attacks. 5. Conduct regular security audits and penetration testing focusing on web application inputs and third-party plugins. 6. Educate web developers and administrators on secure coding practices related to input handling and output encoding. 7. Consider temporarily disabling or replacing the vulnerable plugin if immediate patching is not feasible. 8. Monitor web server logs and user reports for signs of suspicious activity indicative of XSS exploitation attempts.