CVE-2025-58871 is a Stored Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the Luis Rock product 'Master Paper Collapse Toggle' up to version 1.1. Stored XSS occurs when malicious input is improperly neutralized during web page generation and is persistently stored on the target server, later served to users without adequate sanitization or encoding. This vulnerability allows an attacker with low privileges (PR:L) and requiring user interaction (UI:R) to inject malicious scripts that execute in the context of other users' browsers. The CVSS v3.1 base score is 6.5 (medium severity), reflecting network attack vector (AV:N), low attack complexity (AC:L), partial confidentiality, integrity, and availability impacts (C:L/I:L/A:L), and scope change (S:C). The vulnerability can lead to theft of user credentials, session hijacking, defacement, or unauthorized actions performed on behalf of users. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability affects all versions up to 1.1, with no specific earliest affected version identified. The issue arises from improper input validation and output encoding during dynamic web page generation, allowing malicious payloads to be stored and executed when other users access the affected pages or components.

For European organizations using the 'Master Paper Collapse Toggle' product, this vulnerability poses a significant risk to web application security and user trust. Exploitation could lead to unauthorized access to sensitive information, including user credentials and session tokens, potentially resulting in account takeover and data breaches. The partial impact on confidentiality, integrity, and availability means attackers could manipulate displayed content, inject fraudulent information, or disrupt normal operations. Given the stored nature of the XSS, multiple users could be affected once the malicious payload is stored. This risk is particularly critical for organizations handling personal data under GDPR, as exploitation could lead to regulatory non-compliance and financial penalties. Additionally, phishing campaigns leveraging this vulnerability could target European users, increasing the risk of broader social engineering attacks. The requirement for low privileges and user interaction lowers the barrier for exploitation, making it a realistic threat in environments where this product is deployed.

1. Immediate mitigation should include implementing strict input validation and output encoding on all user-supplied data within the 'Master Paper Collapse Toggle' application, especially in areas where content is stored and later rendered. 2. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS payloads. 3. Conduct a thorough code review and security audit of the affected product versions to identify and remediate all instances of improper input handling. 4. Monitor web application logs for unusual or suspicious input patterns that may indicate attempted exploitation. 5. Educate users and administrators about the risks of XSS and encourage cautious interaction with unexpected or suspicious content. 6. Since no patches are currently linked, coordinate with the vendor Luis Rock for timely updates and apply patches as soon as they become available. 7. Consider deploying Web Application Firewalls (WAFs) with rules tailored to detect and block XSS attack patterns specific to this vulnerability. 8. For organizations unable to immediately patch, restrict access to the vulnerable components or disable features related to 'Master Paper Collapse Toggle' until remediation is complete.