CVE-2025-9095 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 the REST endpoint component, within the library file lib/rest/routes/users.js. The flaw allows an attacker to manipulate input that is insufficiently sanitized or validated, leading to the injection and execution of malicious scripts in the context of a victim's browser. This type of vulnerability can be exploited remotely without requiring authentication, although user interaction is necessary to trigger the malicious script, such as by convincing a user to visit a crafted URL or interact with a malicious payload. The vulnerability has been publicly disclosed, but the vendor has not responded or issued a patch as of the publication date (August 17, 2025). The CVSS v4.0 base score is 5.1, indicating a medium severity level. The attack vector is network-based (remote), with low attack complexity and no privileges required, but user interaction is needed to exploit the vulnerability. The impact primarily affects confidentiality and integrity to a limited extent, as the attacker can execute scripts in the victim's browser, potentially leading to session hijacking, credential theft, or unauthorized actions within the web application context. Availability is not impacted. No known exploits are currently reported in the wild, but public disclosure increases the risk of exploitation attempts. The absence of vendor patches or mitigations increases the urgency for affected organizations to implement compensating controls.

For European organizations using ExpressGateway express-gateway versions 1.16.0 to 1.16.10, this vulnerability poses a risk of client-side attacks that can compromise user sessions, steal sensitive information, or perform unauthorized actions on behalf of users. Since ExpressGateway is often used as an API gateway or microservices management tool, exploitation could lead to broader security issues if attackers leverage stolen credentials or session tokens to access backend services. The impact is particularly significant for organizations handling sensitive personal data or critical business operations, as XSS attacks can facilitate data breaches or unauthorized data manipulation. Additionally, regulatory frameworks such as GDPR impose strict requirements on data protection; a successful attack exploiting this vulnerability could lead to compliance violations and associated penalties. The lack of vendor response and patches means European organizations must proactively assess their exposure and implement mitigations to reduce risk. The medium severity rating suggests the threat is moderate but should not be underestimated, especially in environments with high-value targets or sensitive user bases.

Given the absence of official patches, European organizations should implement the following specific mitigations: 1) Conduct an immediate inventory to identify all instances of ExpressGateway express-gateway in use, focusing on versions 1.16.0 through 1.16.10. 2) Apply strict input validation and output encoding on all user-supplied data processed by the REST endpoints, particularly those related to user management routes. 3) Deploy Web Application Firewalls (WAFs) with custom rules designed to detect and block common XSS attack patterns targeting the vulnerable endpoints. 4) Implement Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers interacting with the gateway. 5) Educate users and administrators about the risk of phishing or social engineering attacks that could trigger XSS exploitation. 6) Monitor logs and network traffic for unusual activities or attempted exploitation patterns. 7) Plan for an upgrade or replacement strategy to move to a patched or alternative gateway solution once available. 8) Isolate the express-gateway deployment within network segments with limited exposure to untrusted networks to reduce attack surface. These measures go beyond generic advice by focusing on compensating controls tailored to the specific vulnerability context and product usage.