CVE-2025-57926 is a stored Cross-site Scripting (XSS) vulnerability identified in the WordPress plugin Passster developed by WP Chill. The vulnerability stems from improper neutralization of input during web page generation, classified under CWE-79. This flaw allows an attacker with at least low-level privileges (PR:L) and requiring user interaction (UI:R) to inject malicious scripts that are stored persistently within the application. When other users or administrators view the affected pages, the malicious script executes in their browsers, potentially leading to session hijacking, privilege escalation, or unauthorized actions. The vulnerability affects all versions of Passster up to and including 4.2.18. The CVSS v3.1 base score is 6.5 (medium severity), reflecting network attack vector (AV:N), low attack complexity (AC:L), partial privileges required, and a scope change (S:C) indicating that the vulnerability affects resources beyond the initially compromised component. The impact includes partial confidentiality, integrity, and availability loss. No known exploits are currently in the wild, and no patches have been linked yet, indicating that mitigation may rely on vendor updates or workarounds. Passster is a WordPress plugin used to protect content with passwords, commonly deployed on websites requiring content access control. The stored XSS vulnerability could be exploited by authenticated users with limited privileges to inject scripts that affect higher-privileged users or site visitors, making it a significant threat vector in multi-user WordPress environments.

For European organizations, especially those using WordPress with the Passster plugin to protect sensitive or restricted content, this vulnerability poses a risk of unauthorized data exposure, session hijacking, and potential site defacement or redirection. The stored XSS can lead to compromise of administrator accounts if they interact with malicious payloads, resulting in broader site control loss. This can disrupt business operations, damage reputation, and lead to regulatory non-compliance under GDPR if personal data is exposed or manipulated. The medium severity score reflects that while exploitation requires some privileges and user interaction, the scope change means the impact can extend beyond the initially compromised user. Organizations running multi-user WordPress sites with Passster are at particular risk, including educational institutions, government portals, and e-commerce platforms in Europe that rely on content protection. The absence of known exploits suggests a window for proactive mitigation, but also means attackers could develop exploits in the future.

European organizations should immediately audit their WordPress installations for the presence of the Passster plugin and verify the version in use. Until an official patch is released, administrators should consider disabling the plugin or restricting its use to trusted users only. Implementing strict input validation and output encoding on all user-generated content related to Passster can reduce the risk of XSS. Employing Web Application Firewalls (WAFs) with rules targeting XSS payloads can provide temporary protection. Additionally, enforcing the principle of least privilege by limiting user roles that can input content into Passster-protected areas reduces attack surface. Monitoring logs for unusual script injections or user behavior indicative of exploitation attempts is recommended. Once a patch is available, prompt application of updates is critical. Organizations should also educate users about the risks of interacting with suspicious content and ensure that browser security features like Content Security Policy (CSP) are configured to mitigate script injection impacts.