CVE-2025-55579 is a Cross Site Scripting (XSS) vulnerability identified in SolidInvoice version 2.3.7, specifically within the Tax Rate functionality. SolidInvoice is an open-source invoicing application used by businesses to manage billing and invoicing processes. The vulnerability allows an attacker to inject malicious scripts into the Tax Rate input fields, which are then executed in the context of the victim's browser when viewing or interacting with affected pages. This type of vulnerability typically arises due to insufficient input validation or output encoding, enabling attackers to execute arbitrary JavaScript code. Such exploitation can lead to session hijacking, credential theft, unauthorized actions on behalf of the user, or delivery of further malware. The issue was addressed and fixed in version 2.3.8 of SolidInvoice. There are no known public exploits in the wild at this time, and no CVSS score has been assigned yet. However, the vulnerability's presence in a financial application that handles sensitive billing data elevates its potential risk. The lack of authentication requirements or user interaction details is not specified, but given the nature of XSS, it typically requires the victim to access a maliciously crafted page or input. The vulnerability affects users running version 2.3.7 or earlier, and upgrading to 2.3.8 or later is necessary to remediate the issue.

For European organizations using SolidInvoice 2.3.7 or earlier, this XSS vulnerability poses a significant risk to the confidentiality and integrity of invoicing and financial data. Attackers exploiting this flaw could steal session cookies, enabling unauthorized access to invoicing dashboards, manipulate billing information, or conduct fraudulent transactions. This could lead to financial losses, reputational damage, and regulatory compliance issues, especially under GDPR where data protection is stringent. The availability impact is generally low for XSS, but indirect denial of service or disruption could occur if attackers leverage the vulnerability to inject disruptive scripts. Since invoicing systems are critical for business operations, any compromise could disrupt financial workflows. The absence of known exploits suggests a window of opportunity for organizations to patch before active exploitation. However, the financial nature of the application and the potential for phishing or social engineering attacks leveraging this vulnerability increase the threat level for European businesses reliant on SolidInvoice.

Organizations should immediately upgrade SolidInvoice installations to version 2.3.8 or later, where the vulnerability has been fixed. In addition to patching, organizations should implement strict input validation and output encoding on all user-supplied data fields, especially those related to financial inputs like Tax Rates. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. Conduct regular security audits and penetration testing focused on web application vulnerabilities, including XSS. Educate users and administrators about the risks of clicking on suspicious links or inputs that could exploit XSS. Monitor web application logs for unusual input patterns or error messages that could indicate attempted exploitation. If upgrading is temporarily not possible, consider applying web application firewall (WAF) rules to detect and block malicious payloads targeting the Tax Rate functionality. Finally, maintain an incident response plan to quickly address any detected exploitation attempts.