CVE-2025-5398 is a stored Cross-Site Scripting (XSS) vulnerability affecting the Ninja Forms WordPress plugin, developed by kstover, which is widely used for building contact forms. This vulnerability exists in all versions up to and including 3.10.2.1. The root cause is insufficient output escaping of user-supplied data passed through the plugin's templating engine. Specifically, authenticated users with contributor-level permissions or higher can inject malicious JavaScript code into form pages. When any user accesses a page containing the injected script, the malicious code executes in their browser context. This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). The CVSS v3.1 base score is 6.4, indicating a medium severity level. The attack vector is network-based (AV:N), with low attack complexity (AC:L), requiring privileges (PR:L) but no user interaction (UI:N). The scope is changed (S:C), meaning the vulnerability can affect resources beyond the initially vulnerable component. The impact affects confidentiality and integrity but not availability. No known exploits are currently reported in the wild. The vulnerability allows an attacker to potentially steal session cookies, perform actions on behalf of other users, or conduct phishing attacks within the context of the vulnerable site. Since the vulnerability requires authenticated access at contributor level or above, it limits exploitation to users who already have some level of trust or access within the WordPress environment. However, many WordPress sites allow contributors or editors, making this a significant risk if such roles are assigned to untrusted users or if accounts are compromised.

For European organizations using WordPress sites with the Ninja Forms plugin, this vulnerability poses a risk of unauthorized script execution leading to session hijacking, data theft, or privilege escalation within the site. This can compromise the confidentiality and integrity of user data and site content. Organizations handling sensitive or personal data (e.g., e-commerce, healthcare, government portals) are particularly at risk due to potential data leakage or defacement. The vulnerability could also be leveraged to distribute malware or phishing content to site visitors, damaging reputation and trust. Given the widespread use of WordPress in Europe, including by SMEs and public sector entities, the impact could be broad. The requirement for contributor-level access reduces the risk from external anonymous attackers but raises concerns about insider threats or compromised accounts. Additionally, the changed scope means that exploitation could affect other components or users beyond the initial injection point, increasing potential damage. The absence of known exploits in the wild suggests that proactive patching and mitigation can prevent incidents. However, delayed remediation could lead to targeted attacks, especially in sectors with high-value data or critical services.

1. Immediate update of the Ninja Forms plugin to a patched version once released by the vendor. Since no patch links are currently available, organizations should monitor vendor advisories closely. 2. Restrict contributor-level and higher permissions to trusted users only; review and audit user roles regularly to minimize risk. 3. Implement Web Application Firewall (WAF) rules to detect and block suspicious input patterns related to script injection in form submissions. 4. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts on affected web pages. 5. Conduct regular security audits and penetration testing focusing on user input handling in WordPress plugins. 6. Educate site administrators and content managers about the risks of XSS and the importance of role-based access control. 7. Monitor logs for unusual activity indicative of exploitation attempts, such as unexpected script payloads or anomalous user behavior. 8. Consider temporary disabling or replacing the Ninja Forms plugin with alternative form builders that do not have this vulnerability until a patch is available.