CVE-2025-9169 is a cross-site scripting (XSS) vulnerability identified in SolidInvoice versions up to 2.4.0, specifically within the Quote Module's /quotes endpoint. The vulnerability arises from improper sanitization or validation of the 'Name' argument, allowing an attacker to inject malicious scripts. This flaw enables remote exploitation without requiring authentication, although user interaction is necessary for the malicious payload to execute (e.g., a victim clicking a crafted link). The vulnerability has a CVSS 4.0 base score of 5.1, indicating medium severity. The attack vector is network-based with low attack complexity and no privileges required, but user interaction is needed. The impact primarily affects the confidentiality and integrity of user sessions or data accessible via the web interface, potentially allowing attackers to steal session cookies, perform actions on behalf of users, or deface web content. The vendor has not responded to early disclosure attempts, and no patches or mitigations have been published yet. While no known exploits are currently active in the wild, the public disclosure increases the risk of exploitation by opportunistic attackers.

For European organizations using SolidInvoice for invoicing and financial management, this XSS vulnerability poses a risk of session hijacking, unauthorized actions, and data exposure through client-side script execution. Given that invoicing systems handle sensitive financial data and client information, exploitation could lead to data breaches, fraud, or reputational damage. The remote nature of the vulnerability means attackers can target exposed SolidInvoice instances over the internet. The requirement for user interaction suggests phishing or social engineering could be used to deliver the exploit. Organizations in Europe with web-facing SolidInvoice deployments, especially those lacking robust input validation or web application firewalls, are at risk. Additionally, the lack of vendor response and patches increases the window of exposure. Compliance with GDPR also means that any data breach resulting from exploitation could lead to regulatory penalties.

1. Immediately restrict external access to the SolidInvoice /quotes endpoint by implementing network-level controls such as IP whitelisting or VPN access. 2. Employ web application firewalls (WAFs) with rules to detect and block common XSS payloads targeting the 'Name' parameter. 3. Sanitize and validate all user inputs on the server side, especially the 'Name' argument in the Quote Module, using strict allowlists or encoding outputs to prevent script injection. 4. Educate users about phishing risks and suspicious links to reduce the likelihood of successful user interaction exploitation. 5. Monitor logs for unusual requests or error patterns related to the /quotes endpoint. 6. If possible, upgrade to a version of SolidInvoice that addresses this vulnerability once released or consider applying community-developed patches. 7. Implement Content Security Policy (CSP) headers to reduce the impact of potential XSS attacks by restricting script execution sources. 8. Regularly review and update incident response plans to include scenarios involving web application vulnerabilities like XSS.