CVE-2025-23904 is a high-severity reflected Cross-site Scripting (XSS) vulnerability identified in the NotFound Rebrand Fluent Forms product. This vulnerability arises due to improper neutralization of input during web page generation, classified under CWE-79. Specifically, the flaw allows an attacker to inject malicious scripts into web pages generated by the vulnerable versions of Rebrand Fluent Forms (up to version 1.0). When a user interacts with a crafted URL or input that triggers this vulnerability, the malicious script executes in the context of the victim's browser. This can lead to unauthorized actions such as session hijacking, defacement, or redirection to malicious sites. The CVSS v3.1 score of 7.1 reflects the vulnerability's characteristics: it can be exploited remotely over the network (AV:N), requires no privileges (PR:N), but does require user interaction (UI:R). The scope is changed (S:C), indicating that exploitation can affect resources beyond the vulnerable component. The impact includes low confidentiality, integrity, and availability losses, meaning that while the attacker may not gain full control, they can still perform impactful malicious actions. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that mitigation may rely on vendor updates or temporary workarounds. The vulnerability was reserved in January 2025 and published in March 2025, showing recent discovery and disclosure. Given the nature of reflected XSS, the attack vector typically involves tricking users into clicking malicious links or submitting crafted inputs that the vulnerable form processes without proper sanitization or encoding.

For European organizations, this vulnerability poses a significant risk especially for those relying on the Rebrand Fluent Forms plugin for web forms on their public-facing websites. Successful exploitation can lead to session hijacking, theft of sensitive user data, or unauthorized actions performed on behalf of legitimate users. This can damage organizational reputation, lead to regulatory non-compliance (e.g., GDPR breaches if personal data is exposed), and potentially cause financial losses. Since the vulnerability requires user interaction, phishing campaigns targeting employees or customers could leverage this flaw to escalate attacks. Additionally, the scope change (S:C) implies that the impact could extend beyond the vulnerable component, potentially affecting other integrated systems or services. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate it, as attackers often develop exploits rapidly after public disclosure. European organizations with high web traffic and customer interaction through forms are particularly at risk, as the attack surface is larger. The vulnerability also increases the attack surface for supply chain attacks if the plugin is widely used by third-party service providers.

1. Immediate mitigation should focus on input validation and output encoding: implement strict server-side input sanitization to neutralize potentially malicious scripts before rendering user inputs in web pages. 2. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. 3. Monitor web traffic for suspicious URLs or payloads targeting the vulnerable forms, and deploy Web Application Firewalls (WAFs) with custom rules to detect and block reflected XSS attempts. 4. Educate users and employees about the risks of clicking on untrusted links, especially those that could trigger reflected XSS attacks. 5. Coordinate with the vendor (NotFound) to obtain patches or updates as soon as they become available; prioritize patching vulnerable systems promptly. 6. If patching is delayed, consider temporarily disabling or replacing the vulnerable form component with alternative secure solutions. 7. Conduct regular security assessments and penetration testing focused on web application input handling to identify similar vulnerabilities proactively. 8. Review and enhance incident response plans to quickly address potential exploitation attempts involving this vulnerability.