CVE-2025-49866 is a high-severity reflected Cross-site Scripting (XSS) vulnerability identified in the Nikel Beautiful Cookie Consent Banner product, affecting versions up to 4.6.1. This vulnerability arises from improper neutralization of input during web page generation (CWE-79), allowing attackers to inject malicious scripts into web pages that utilize this cookie consent banner. Specifically, the flaw enables reflected XSS attacks, where malicious payloads are embedded in URLs or other input vectors and reflected back in the HTTP response without proper sanitization or encoding. The vulnerability has a CVSS 3.1 base score of 7.1, indicating a high impact with an attack vector of network (remote exploitation), low attack complexity, no privileges required, but requiring user interaction (clicking a crafted link). The scope is changed (S:C), meaning the vulnerability can affect resources beyond the vulnerable component. The impact affects confidentiality, integrity, and availability at a low level, as the injected scripts can steal sensitive information, manipulate page content, or perform actions on behalf of the user. No known exploits are currently reported in the wild, and no patches or fixes have been linked yet. The vulnerability was published on July 4, 2025, and reserved on June 11, 2025. The reflected XSS in a cookie consent banner is particularly concerning because such banners are present on virtually all websites to comply with privacy regulations, making this a widespread potential attack surface if the vulnerable product is widely deployed.

For European organizations, the impact of CVE-2025-49866 can be significant due to the widespread use of cookie consent banners driven by GDPR and other privacy laws. Exploitation of this vulnerability could allow attackers to execute malicious scripts in the context of the affected websites, leading to theft of user credentials, session hijacking, or unauthorized actions performed on behalf of users. This can result in data breaches, loss of user trust, regulatory penalties, and reputational damage. Since the vulnerability affects the cookie consent banner component, which is loaded on virtually every page, the attack surface is large, increasing the risk of successful exploitation. Additionally, the reflected XSS can be used as a vector for phishing or delivering malware payloads. European organizations handling sensitive personal data or financial transactions are especially at risk, as attackers could leverage this vulnerability to bypass security controls or exfiltrate data. The vulnerability's presence in a privacy compliance tool ironically undermines the security posture of organizations relying on it.

1. Immediate mitigation should include disabling or replacing the Nikel Beautiful Cookie Consent Banner with a secure alternative that properly sanitizes and encodes all user inputs before rendering them on web pages. 2. Implement Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. 3. Conduct thorough input validation and output encoding on all user-controllable inputs, especially those reflected in the cookie consent banner. 4. Monitor web traffic and logs for suspicious URL patterns or payloads that may indicate attempted exploitation. 5. Educate web developers and security teams about secure coding practices related to XSS prevention. 6. Once available, promptly apply official patches or updates from Nikel addressing this vulnerability. 7. Consider implementing Web Application Firewalls (WAFs) with rules to detect and block reflected XSS payloads targeting the cookie consent banner. 8. Review and audit third-party components integrated into websites to ensure they meet security standards before deployment.