CVE-2025-49912 identifies a stored cross-site scripting (XSS) vulnerability in the Nks Email Subscription Popup plugin, versions up to 1.2.26. This vulnerability stems from improper neutralization of input during web page generation, meaning that user-supplied data is not adequately sanitized before being embedded into web pages. As a result, an attacker with authenticated access can inject malicious JavaScript payloads that are stored persistently within the plugin's data store. When other users or administrators view the affected pages, the malicious scripts execute in their browsers, potentially leading to session hijacking, credential theft, defacement, or further exploitation of the affected web application. The CVSS vector indicates the attack requires network access (AV:N), low attack complexity (AC:L), but requires privileges (PR:H) and user interaction (UI:R). The scope is changed (S:C), meaning the vulnerability affects components beyond the initially vulnerable component. The impact on confidentiality, integrity, and availability is low to medium (C:L/I:L/A:L). No public exploits have been reported yet, and no patches are currently available, though the vulnerability was reserved in June 2025 and published in October 2025. The plugin is commonly used in WordPress environments to manage email subscriptions via popups, making it a target for attackers seeking to compromise websites with user engagement features.

For European organizations, this vulnerability poses a moderate risk, especially for those operating customer-facing websites that use the Nks Email Subscription Popup plugin. Exploitation could allow attackers to execute arbitrary scripts in the context of the affected site, leading to theft of user credentials, session tokens, or other sensitive information. This can result in unauthorized access to user accounts, data breaches, or reputational damage. Additionally, attackers could deface websites or redirect users to malicious sites, impacting brand trust and compliance with data protection regulations such as GDPR. The requirement for authenticated access limits the attack surface but does not eliminate risk, as attackers may leverage social engineering or compromised credentials. The vulnerability also affects availability to a limited extent by potentially disrupting normal website functionality. Organizations with high volumes of user interaction or those in sectors like e-commerce, finance, or healthcare should be particularly vigilant.

Organizations should immediately audit their web environments to identify installations of the Nks Email Subscription Popup plugin and determine the versions in use. Until an official patch is released, consider disabling or removing the plugin to eliminate exposure. Implement strict input validation and output encoding on all user-supplied data within the plugin's scope to prevent script injection. Employ web application firewalls (WAFs) with rules designed to detect and block XSS payloads targeting this plugin. Monitor logs and user activity for signs of suspicious behavior or exploitation attempts. Educate administrators and users about the risks of phishing and credential compromise to reduce the likelihood of attackers gaining authenticated access. Once a patch becomes available, prioritize its deployment and verify the effectiveness of the fix through security testing. Additionally, review and harden authentication mechanisms to reduce privilege escalation risks.