CVE-2025-55580 is a Cross Site Scripting (XSS) vulnerability affecting SolidInvoice versions 2.3.7 and 2.3.8. SolidInvoice is an open-source invoicing system used by businesses to manage client billing and invoicing. The vulnerability exists within the client-related functionality, which likely involves user input fields that are not properly sanitized or encoded before being rendered in the web interface. This flaw allows an attacker to inject malicious scripts into the web pages viewed by other users, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. Although no specific details about the exact input vectors or affected parameters are provided, the presence of XSS in client functionality suggests that attackers could exploit this vulnerability by tricking users into clicking crafted links or submitting malicious data that gets stored or reflected in the application interface. The vulnerability was reserved on August 13, 2025, and published on August 29, 2025, but no CVSS score or known exploits in the wild have been reported yet. The absence of a patch link indicates that a fix might not have been released at the time of this report, increasing the risk for organizations still running the vulnerable versions. Given the nature of XSS, the attack requires user interaction, but does not require authentication if the vulnerable functionality is accessible publicly or to authenticated users with lower privileges. The impact primarily affects confidentiality and integrity, as attackers can steal sensitive information or manipulate the user interface to perform unauthorized actions. Availability impact is generally low for XSS vulnerabilities unless combined with other exploits.

For European organizations using SolidInvoice 2.3.7 or 2.3.8, this XSS vulnerability poses a significant risk to client data confidentiality and integrity. Attackers exploiting this flaw could hijack user sessions, steal authentication tokens, or perform actions on behalf of legitimate users, potentially leading to financial fraud, data leakage, or reputational damage. Since invoicing systems handle sensitive financial and client information, exploitation could result in regulatory compliance violations under GDPR if personal data is compromised. The lack of a patch increases exposure, especially for small and medium enterprises that may not have robust security monitoring or rapid update processes. Additionally, phishing campaigns leveraging this vulnerability could target European clients or partners, amplifying the threat. While no known exploits exist yet, the public disclosure of this vulnerability may prompt attackers to develop exploits, increasing the urgency for mitigation. The impact on availability is minimal, but the risk to business operations and trustworthiness is considerable.

European organizations should immediately assess their use of SolidInvoice and identify any installations running versions 2.3.7 or 2.3.8. In the absence of an official patch, organizations should implement the following mitigations: 1) Apply Web Application Firewall (WAF) rules to detect and block typical XSS attack patterns targeting the invoicing system. 2) Conduct input validation and output encoding on all client-related input fields within SolidInvoice, if possible, by customizing or hardening the application code. 3) Restrict access to the invoicing system to trusted networks or VPNs to reduce exposure. 4) Educate users about the risks of clicking suspicious links or submitting untrusted data. 5) Monitor logs for unusual activities or repeated attempts to inject scripts. 6) Plan for an upgrade to a patched version once available, or consider alternative invoicing solutions with active security support. 7) Implement Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in the browser context. These targeted actions go beyond generic advice and focus on reducing attack surface and exposure until a vendor patch is released.