CVE-2025-40720 is a reflected Cross-site Scripting (XSS) vulnerability identified in the Quiter Gateway product, specifically versions prior to 4.7.0. Quiter Gateway is a Java WAR application deployed on Apache Tomcat servers. The vulnerability arises due to improper neutralization of user-supplied input during web page generation, classified under CWE-79. An attacker can exploit this flaw by crafting a malicious URL that injects JavaScript code through the 'campo' parameter in the endpoint /<Client>FacturaE/VerFacturaPDF. When a victim accesses this URL, the injected script executes in their browser context, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The vulnerability does not require authentication and can be triggered remotely with no privileges, but it does require user interaction (clicking or visiting the malicious URL). The CVSS v4.0 base score is 5.1 (medium severity), reflecting network attack vector, low complexity, no privileges required, but user interaction needed and limited scope impact. No known exploits are currently reported in the wild. The vulnerability affects all versions prior to 4.7.0, and no official patches or mitigation links are provided yet. Given the nature of the vulnerability, it primarily threatens the confidentiality and integrity of user sessions and data processed by the affected web application.

For European organizations using Quiter Gateway, this vulnerability poses a moderate risk. Exploitation could lead to unauthorized script execution in users' browsers, enabling attackers to steal sensitive information such as authentication tokens or personal data, manipulate displayed content, or perform actions on behalf of users without their consent. This can result in data breaches, reputational damage, and potential regulatory non-compliance under GDPR if personal data is compromised. Since Quiter Gateway is used for handling electronic invoicing (FacturaE), which is critical for financial and tax processes, disruption or compromise could affect business operations and financial integrity. The medium severity score suggests that while the vulnerability is not trivial, it is not catastrophic; however, the financial and legal implications in Europe, where electronic invoicing is widely adopted and regulated, could be significant. The lack of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers often weaponize such vulnerabilities once publicly disclosed.

European organizations should immediately review their use of Quiter Gateway and verify the version in deployment. Upgrading to version 4.7.0 or later, once available, is the most effective mitigation. In the interim, organizations should implement strict input validation and output encoding on the 'campo' parameter to neutralize malicious scripts. Web Application Firewalls (WAFs) can be configured to detect and block typical XSS payloads targeting this endpoint. Additionally, applying Content Security Policy (CSP) headers can reduce the impact of successful XSS by restricting script execution sources. User awareness training to avoid clicking suspicious links related to electronic invoicing portals is also recommended. Monitoring logs for unusual URL access patterns to /<Client>FacturaE/VerFacturaPDF with suspicious parameters can help detect exploitation attempts. Finally, coordinate with Quiter for official patches and security advisories to ensure timely updates.