CVE-2025-40720 is a reflected Cross-site Scripting (XSS) vulnerability identified in versions prior to 4.7.0 of the Quiter Gateway product, which is a Java WAR application running on Apache Tomcat. The vulnerability arises from improper neutralization of user-supplied input during web page generation, specifically through the 'campo' parameter in the URL path /<Client>FacturaE/VerFacturaPDF. An attacker can craft a malicious URL containing JavaScript code injected into this parameter, which when accessed by a victim, causes the victim's browser to execute the injected script. This reflected XSS does not require prior authentication or privileges and can be exploited remotely by enticing users to click on a malicious link. The CVSS 4.0 base score is 5.1 (medium severity), reflecting that the attack vector is network-based, requires no privileges, no user interaction is needed beyond clicking the link, and the impact is limited to client-side confidentiality and integrity (browser context). There are no known exploits in the wild yet, and no patches have been linked, indicating that mitigation may require updating to version 4.7.0 or later once available or applying custom input validation and output encoding controls. The vulnerability is classified under CWE-79, which is a common and well-understood web application security issue related to failure to properly sanitize input before rendering it in HTML contexts, leading to script injection risks.

For European organizations using Quiter Gateway, especially those handling electronic invoicing or document management via the FacturaE module, this vulnerability poses a risk of client-side script execution. The impact includes potential theft of session cookies, redirection to malicious sites, or execution of arbitrary JavaScript in the context of the victim's browser, which could lead to account compromise, data leakage, or further phishing attacks. Although the vulnerability does not directly compromise server integrity or availability, the exploitation can undermine user trust and lead to reputational damage. Organizations in sectors with high regulatory scrutiny around data protection, such as finance, healthcare, and public administration, may face compliance risks if user data confidentiality is compromised. The medium severity score reflects that while the attack requires user interaction (clicking a malicious link), the ease of exploitation and potential for widespread phishing campaigns make it a relevant threat. Additionally, since Quiter Gateway is deployed on Apache Tomcat, a common Java application server, the exposure surface is significant if the product is widely used in Europe.

To mitigate this vulnerability, European organizations should take the following specific actions: 1) Immediately review and restrict access to the vulnerable endpoint /<Client>FacturaE/VerFacturaPDF, implementing web application firewall (WAF) rules to detect and block suspicious payloads in the 'campo' parameter. 2) Apply strict input validation and output encoding on all user-supplied parameters, particularly 'campo', ensuring that any HTML special characters are properly escaped before rendering. 3) Monitor logs for unusual URL patterns or repeated attempts to exploit this parameter. 4) Coordinate with Quiter to obtain and deploy the official patch or upgrade to version 4.7.0 or later as soon as it becomes available. 5) Educate end users about the risks of clicking unsolicited links, especially those related to invoicing or document portals. 6) Consider implementing Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of XSS attacks. 7) Conduct penetration testing and code reviews focused on input handling in the affected modules to identify any additional injection points.