CVE-2025-3670 is a stored Cross-Site Scripting (XSS) vulnerability affecting the KiwiChat NextClient plugin for WordPress. This vulnerability arises from improper neutralization of input during web page generation, specifically through the 'url' parameter. All versions up to and including 6.2 are affected due to insufficient input sanitization and output escaping. An authenticated attacker with Contributor-level privileges or higher can exploit this flaw by injecting arbitrary JavaScript code into pages served by the plugin. When other users access these compromised pages, the malicious scripts execute in their browsers within the context of the vulnerable site. This can lead to session hijacking, defacement, or redirection to malicious sites. The vulnerability has a CVSS 3.1 base score of 6.4, indicating a medium severity level. The attack vector is network-based (remote), requires low attack complexity, and privileges at the level of an authenticated contributor. No user interaction is required for exploitation once the malicious script is stored. The scope is changed, meaning the vulnerability can affect components beyond the vulnerable plugin itself, potentially impacting the broader WordPress environment. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability is classified under CWE-79, which covers improper neutralization of input leading to XSS attacks.

For European organizations using WordPress sites with the KiwiChat NextClient plugin, this vulnerability poses a significant risk to the confidentiality and integrity of user data. Exploitation can lead to theft of session cookies, enabling attackers to impersonate legitimate users, including administrators. This can result in unauthorized access to sensitive information, manipulation of site content, or further compromise of the hosting environment. The change in scope means that the impact could extend beyond the plugin, potentially affecting other integrated systems or plugins. Given the medium CVSS score and the requirement for authenticated access, the threat is more pronounced in environments where multiple users have contributor-level permissions, such as collaborative corporate websites, educational platforms, or public-facing community portals. The absence of required user interaction for the attack to succeed increases the risk of automated exploitation once an attacker gains contributor access. Although no active exploits are known yet, the vulnerability could be leveraged in targeted attacks against European organizations with strategic or high-profile web assets, potentially damaging reputation and causing operational disruptions.

1. Immediate mitigation should include restricting Contributor-level access to trusted users only, minimizing the number of accounts with such privileges. 2. Implement strict input validation and output encoding on the 'url' parameter within the KiwiChat NextClient plugin code, ideally by applying context-aware escaping functions to neutralize malicious scripts. 3. Monitor and audit user-generated content for suspicious or unexpected script injections, employing automated scanning tools tailored for stored XSS detection. 4. Employ Web Application Firewalls (WAFs) with custom rules to detect and block attempts to inject scripts via the vulnerable parameter. 5. Regularly update WordPress and all plugins, and closely monitor vendor communications for official patches or security advisories related to KiwiChat NextClient. 6. Conduct security awareness training for users with elevated privileges to recognize and prevent misuse of their access. 7. Consider implementing Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts on affected web pages. 8. For organizations with high-risk profiles, perform penetration testing focused on XSS vulnerabilities to identify and remediate similar issues proactively.