CVE-2025-9096 is a cross-site scripting (XSS) vulnerability identified in the ExpressGateway express-gateway product, specifically affecting versions 1.16.0 through 1.16.10. The vulnerability resides in an unspecified function within the REST Endpoint component, located in the library file lib/rest/routes/apps.js. This flaw allows an attacker to remotely inject malicious scripts into web pages served by the vulnerable ExpressGateway instance. The vulnerability does not require authentication (PR:L means privileges required are low) but does require user interaction (UI:P), indicating that the attack vector involves tricking a user into interacting with a crafted payload. The CVSS 4.0 base score is 5.1, categorizing it as a medium severity issue. The attack complexity is low (AC:L), and the vulnerability does not compromise confidentiality or availability but has limited impact on integrity (VI:L). The vendor was notified but has not responded, and no official patches or mitigations have been published yet. While no known exploits are currently in the wild, the public disclosure of the exploit code increases the risk of exploitation. ExpressGateway is an API Gateway solution used to manage and secure APIs, often deployed in microservices architectures and cloud environments. The vulnerability could be exploited by attackers to execute arbitrary JavaScript in the context of users accessing the affected REST endpoints, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user.

For European organizations, the impact of this XSS vulnerability depends on the extent of ExpressGateway deployment within their infrastructure. Organizations using ExpressGateway to manage APIs for internal or external services may face risks of client-side attacks that could compromise user sessions or leak sensitive information. This is particularly critical for sectors handling personal data under GDPR, such as finance, healthcare, and e-commerce, where exploitation could lead to data breaches and regulatory penalties. The vulnerability could also undermine trust in digital services and disrupt business operations if exploited in phishing or social engineering campaigns. Since the vulnerability requires user interaction, the impact is somewhat mitigated but remains significant in environments with high user engagement or where APIs serve web portals. The lack of vendor response and patches increases the window of exposure, necessitating proactive measures by European organizations to protect their assets and comply with data protection regulations.

Given the absence of official patches, European organizations should implement immediate compensating controls. These include: 1) Deploying Web Application Firewalls (WAFs) with custom rules to detect and block malicious payloads targeting the vulnerable REST endpoints. 2) Conducting thorough input validation and output encoding on all user-supplied data at the application layer to neutralize potential XSS payloads. 3) Restricting access to the ExpressGateway management interfaces and REST endpoints via network segmentation, VPNs, or IP whitelisting to reduce exposure. 4) Monitoring logs and network traffic for anomalous requests indicative of exploitation attempts. 5) Educating users about phishing and social engineering risks related to XSS attacks to reduce successful user interaction exploitation. 6) Planning and testing upgrades to newer, patched versions of ExpressGateway as soon as they become available. 7) Employing Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in browsers. These targeted measures go beyond generic advice by focusing on the specific nature of the vulnerability and the operational context of ExpressGateway deployments.