CVE-2025-40616 is a Reflected Cross-Site Scripting (XSS) vulnerability identified in all versions of the Bookgy software, specifically within the /bkg_imprimir_comprobante.php endpoint. The vulnerability arises due to improper neutralization of user input in the 'IDRESERVA' parameter, which is directly reflected in the web page output without adequate sanitization or encoding. This flaw allows an attacker to craft a malicious URL containing JavaScript code embedded in the 'IDRESERVA' parameter. When a victim clicks on this URL, the malicious script executes in their browser context, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The vulnerability is classified under CWE-79, which covers improper input neutralization during web page generation. The CVSS 4.0 base score is 5.1 (medium severity), with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:A), and limited scope impact (S: I). There are no known exploits in the wild at the time of publication, and no patches have been released yet. The vulnerability affects all versions of Bookgy, a software product whose market penetration and usage details are not explicitly provided in the data. The vulnerability does not compromise confidentiality, integrity, or availability directly but can be leveraged to perform client-side attacks that may lead to further compromise depending on the victim's environment and privileges.

For European organizations using Bookgy, this vulnerability poses a risk primarily to end-users who interact with the affected web interface. Successful exploitation can lead to theft of session cookies, user credentials, or execution of arbitrary scripts in the context of the victim’s browser, potentially enabling unauthorized access to user accounts or sensitive information. This can undermine user trust and lead to reputational damage, especially for organizations handling sensitive booking or reservation data. While the direct impact on system integrity or availability is limited, the indirect consequences could include phishing, social engineering, or lateral movement within an organization's network if attackers leverage stolen credentials. The requirement for user interaction (clicking a malicious link) somewhat limits the attack's reach but does not eliminate risk, especially in environments where users may be targeted via spear-phishing campaigns. Given the medium severity and lack of authentication requirements, the vulnerability could be exploited at scale if attackers distribute malicious URLs widely. European organizations in sectors such as travel, hospitality, or any industry relying on Bookgy for booking management are particularly at risk. Additionally, regulatory frameworks like GDPR impose strict requirements on protecting user data, so exploitation could lead to compliance issues and fines.

1. Immediate mitigation should focus on input validation and output encoding: developers should implement proper sanitization of the 'IDRESERVA' parameter to neutralize any embedded scripts before reflecting it in the web page. Use context-aware encoding libraries to prevent script injection. 2. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in the browser, limiting the impact of potential XSS payloads. 3. Educate users and staff about the risks of clicking on suspicious links, especially those received via email or messaging platforms. 4. Monitor web server logs for unusual or suspicious requests targeting the 'IDRESERVA' parameter to detect potential exploitation attempts. 5. Since no patch is currently available, consider implementing web application firewalls (WAF) with rules specifically designed to detect and block XSS payloads targeting this parameter. 6. Plan for a timely update or patch deployment once the vendor releases a fix, and verify the patch effectiveness through security testing. 7. Review and enhance incident response procedures to quickly address any exploitation incidents related to this vulnerability.