CVE-2025-9857 is a stored Cross-Site Scripting (XSS) vulnerability affecting the Heateor Login – Social Login Plugin for WordPress, specifically versions up to and including 1.1.9. The vulnerability arises from improper neutralization of input during web page generation (CWE-79), where the plugin fails to adequately sanitize and escape user-supplied attributes in the 'Heateor_Facebook_Login' shortcode. This flaw allows authenticated users with contributor-level access or higher to inject arbitrary JavaScript code into pages. When other users visit these compromised pages, the injected scripts execute in their browsers, potentially leading to session hijacking, privilege escalation, or redirection to malicious sites. The vulnerability does not require user interaction beyond visiting the infected page and has a CVSS 3.1 base score of 6.4, indicating a medium severity level. The attack vector is network-based with low attack complexity, requiring privileges but no user interaction. The scope is changed because the vulnerability can affect other users beyond the attacker. No known exploits are reported in the wild yet, but the vulnerability is publicly disclosed and should be addressed promptly.

For European organizations using WordPress sites with the Heateor Login – Social Login Plugin, this vulnerability poses a significant risk to website integrity and user trust. Exploitation could lead to unauthorized script execution, enabling attackers to steal session cookies, deface websites, or conduct phishing attacks by injecting malicious content. This can compromise confidentiality and integrity of user data and damage organizational reputation. Given the plugin’s role in social login functionality, attackers might also manipulate authentication flows, potentially facilitating unauthorized access or account takeover. The impact is particularly critical for organizations handling sensitive user information or operating in regulated sectors such as finance, healthcare, or e-commerce within Europe, where data protection compliance is stringent. Additionally, compromised websites can be leveraged to distribute malware or conduct further attacks within the European digital ecosystem.

To mitigate this vulnerability, organizations should immediately update the Heateor Login – Social Login Plugin to a patched version once available. Until a patch is released, restrict contributor-level and higher user permissions to trusted personnel only, minimizing the risk of malicious shortcode injection. Implement Web Application Firewalls (WAFs) with rules targeting XSS payloads specific to the plugin’s shortcode parameters. Conduct thorough input validation and output encoding on all user-supplied data within custom code or themes interacting with the plugin. Regularly audit WordPress user roles and monitor for unusual shortcode usage or content changes. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts. Finally, maintain frequent backups and have an incident response plan ready to address potential exploitation.