CVE-2021-25977 is a stored Cross-Site Scripting (XSS) vulnerability affecting PiranhaCMS, specifically versions 7.0.0 through 9.1.1. The vulnerability arises from improper sanitization of the page title input field. A low-privileged user can create or modify a page with a specially crafted page title containing malicious JavaScript code. When this page is viewed by other users or administrators, the embedded script executes in their browsers within the context of the vulnerable web application. This stored XSS flaw allows an attacker to perform actions such as session hijacking, defacement, or executing arbitrary JavaScript that could lead to further compromise of user accounts or the application environment. The vulnerability requires user interaction in the form of viewing the malicious page, and the attacker must have at least low-level privileges to inject the payload. The CVSS 3.1 base score is 5.4 (medium severity), reflecting network attack vector, low attack complexity, low privileges required, and user interaction needed. The impact includes limited confidentiality and integrity loss but no direct impact on availability. No known public exploits have been reported, and no official patches are linked in the provided data, indicating that mitigation may rely on manual sanitization or updates from the vendor. The vulnerability is categorized under CWE-79, a common web application security issue related to improper input validation and output encoding.

For European organizations using PiranhaCMS versions 7.0.0 to 9.1.1, this vulnerability poses a risk primarily to the confidentiality and integrity of web application data and user sessions. Attackers with low privileges could inject malicious scripts that execute in the browsers of other users, potentially leading to session hijacking, unauthorized actions, or data exposure. This could result in reputational damage, loss of customer trust, and compliance issues under regulations such as GDPR if personal data is compromised. While the vulnerability does not directly affect system availability, the indirect consequences of a successful attack could disrupt business operations or lead to further exploitation. Organizations relying on PiranhaCMS for public-facing websites or internal portals should be particularly cautious, as attackers could leverage this vulnerability to escalate privileges or move laterally within the network. The medium severity rating suggests that while the threat is significant, it is not critical, but it should not be ignored given the potential for chained attacks.

1. Upgrade PiranhaCMS to the latest version beyond 9.1.1 where this vulnerability is fixed, as vendor patches are the most reliable mitigation. 2. If immediate upgrade is not possible, implement strict input validation and output encoding on the page title field to neutralize malicious scripts. 3. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers accessing the CMS. 4. Limit the privileges of users who can create or edit pages to trusted personnel only, reducing the attack surface. 5. Conduct regular security audits and penetration testing focused on input fields to detect similar injection flaws. 6. Monitor web application logs for unusual activity or injection attempts targeting page titles. 7. Educate administrators and users about the risks of XSS and encourage cautious behavior when interacting with CMS content. 8. Consider deploying Web Application Firewalls (WAF) with rules tailored to detect and block XSS payloads targeting PiranhaCMS.