CVE-2025-13898 is a stored Cross-Site Scripting (XSS) vulnerability identified in the Ultra Skype Button plugin for WordPress, developed by sozan45. The vulnerability exists due to improper neutralization of input during web page generation, specifically through the 'btn_id' parameter of the [ultra_skype] shortcode. All versions up to and including 1.0 are affected. Authenticated users with Contributor-level access or higher can exploit this flaw by injecting arbitrary JavaScript code into WordPress pages or posts via the shortcode parameter. Because the injected script is stored persistently, it executes in the context of any user who views the infected page, potentially compromising user sessions, stealing cookies, or performing unauthorized actions on behalf of the user. The vulnerability is classified under CWE-79, reflecting improper input sanitization and output escaping. The CVSS v3.1 base score is 6.4, reflecting network attack vector, low attack complexity, requiring privileges (Contributor or above), no user interaction, and a scope change with limited confidentiality and integrity impact but no availability impact. No public exploits are currently known, and no patches have been officially released at the time of publication. The vulnerability was reserved on December 2, 2025, and published on December 6, 2025. The plugin's widespread use in WordPress sites makes this a relevant threat, especially for organizations relying on this plugin for Skype integration on their websites.

For European organizations, this vulnerability poses a moderate risk primarily to the confidentiality and integrity of web applications using the Ultra Skype Button plugin. Attackers with Contributor-level access can inject malicious scripts that execute in the browsers of site visitors, potentially leading to session hijacking, credential theft, or unauthorized actions performed with the victim's privileges. This can result in reputational damage, data breaches, and unauthorized access to sensitive information. Since the attack requires authenticated access, insider threats or compromised contributor accounts are the main vectors. The vulnerability does not affect availability but can facilitate further attacks or persistent compromise. Organizations with public-facing WordPress sites using this plugin are at risk, especially those with multiple contributors or less stringent access controls. The impact is magnified in sectors with strict data protection regulations like GDPR, where data leakage can lead to significant fines and legal consequences.

1. Immediately restrict Contributor-level user privileges to trusted personnel only and review existing contributor accounts for suspicious activity. 2. Disable or remove the Ultra Skype Button plugin if it is not essential to reduce the attack surface. 3. Implement strict input validation and output escaping for all shortcode parameters, especially 'btn_id', to prevent script injection. 4. Monitor WordPress site content for unexpected or suspicious shortcode usage or injected scripts. 5. Apply web application firewall (WAF) rules to detect and block malicious payloads targeting the shortcode parameter. 6. Keep WordPress core and all plugins updated; monitor for official patches or updates from the plugin vendor addressing this vulnerability. 7. Educate content contributors about the risks of injecting untrusted content and enforce secure content management policies. 8. Conduct regular security audits and penetration tests focusing on plugin vulnerabilities and user privilege abuse.