CVE-2025-9856 is a stored Cross-Site Scripting (XSS) vulnerability identified in the Popup Builder WordPress plugin, which is widely used for creating marketing popups. The vulnerability arises from improper neutralization of input during web page generation, specifically within the 'sg_popup' shortcode. Versions up to and including 4.4.1 fail to adequately sanitize and escape user-supplied attributes, enabling authenticated users with contributor-level privileges or higher to inject arbitrary JavaScript code. This malicious code is stored persistently and executed in the context of any user who visits the compromised page, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The vulnerability does not require user interaction but does require the attacker to have authenticated access with contributor or higher privileges, which is a moderate barrier but still significant in multi-user WordPress environments. The CVSS 3.1 base score of 6.4 reflects a medium severity, considering the network attack vector, low attack complexity, and privileges required. No public exploits have been reported yet, but the vulnerability poses a risk especially to websites relying on this plugin for marketing purposes. The stored nature of the XSS increases the potential impact as the malicious payload can affect multiple users over time. The vulnerability was publicly disclosed on December 13, 2025, and no official patch links are currently available, indicating that organizations must apply interim mitigations until a fix is released.

For European organizations, this vulnerability can lead to significant security risks including unauthorized access to user sessions, theft of sensitive information, and potential defacement or manipulation of website content. Marketing and e-commerce websites using the Popup Builder plugin are particularly at risk, as attackers can exploit the trust users place in these sites to execute malicious scripts. This can damage brand reputation, lead to regulatory non-compliance under GDPR due to data breaches, and cause financial losses. The requirement for contributor-level access means insider threats or compromised accounts pose a realistic attack vector. The stored XSS can affect all visitors to an infected page, amplifying the scope of impact. Given the widespread use of WordPress in Europe, especially among SMEs and digital marketing agencies, the threat is non-trivial. Additionally, the cross-site scripting can be leveraged to deliver further attacks such as phishing or malware distribution, increasing the overall risk profile.

1. Monitor for updates from the Popup Builder plugin vendor and apply patches immediately once available. 2. Restrict contributor-level access strictly to trusted users and review user permissions regularly to minimize risk exposure. 3. Implement a Web Application Firewall (WAF) with robust XSS detection and blocking capabilities to filter malicious payloads in shortcode inputs. 4. Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts on affected web pages. 5. Conduct regular security audits and code reviews of user-generated content handling, especially shortcodes and input fields. 6. Educate site administrators and content contributors about the risks of XSS and safe content practices. 7. Use security plugins that sanitize and validate shortcode inputs as an additional layer of defense. 8. Monitor web server and application logs for unusual shortcode usage or script injection attempts. 9. Consider disabling or limiting the use of the vulnerable shortcode until a patch is available. 10. Backup website data regularly to enable quick recovery in case of compromise.