CVE-2025-11276 identifies a cross-site scripting vulnerability in the Comment/Guestbook component of the Rebuild software, affecting versions 4.1.0 through 4.1.3. This vulnerability arises from improper input validation or output encoding in the affected component, allowing an attacker to inject malicious JavaScript code remotely. The attack vector is network-based with no authentication required, but user interaction is necessary to execute the malicious script, typically by tricking a user into clicking a crafted link or viewing a manipulated comment. The vulnerability impacts the confidentiality and integrity of user sessions by enabling potential session hijacking, credential theft, or content manipulation. The CVSS 4.0 base score of 5.1 reflects a medium severity, considering the ease of exploitation (low complexity), no privileges required, but requiring user interaction and limited impact on availability. The vendor has confirmed the flaw and released a fix in version 4.1.4, which addresses the input validation issues. No public exploits have been reported, indicating limited active exploitation. The vulnerability is relevant for organizations using Rebuild for web applications that allow user-generated content, especially where comments or guestbook features are enabled.

For European organizations, this vulnerability poses a moderate risk primarily to web applications leveraging the Rebuild platform with the vulnerable Comment/Guestbook component. Successful exploitation could lead to session hijacking, unauthorized actions performed on behalf of users, or defacement of web content, potentially damaging organizational reputation and user trust. Confidential data accessible through user sessions could be compromised, and integrity of displayed content could be undermined. While availability impact is negligible, the breach of confidentiality and integrity could violate GDPR requirements, leading to regulatory scrutiny and fines. Organizations with high volumes of user interaction on public-facing sites are at greater risk. The lack of known exploits reduces immediate threat, but the ease of exploitation and remote attack vector necessitate prompt remediation to prevent opportunistic attacks. The medium severity suggests prioritization but not emergency response, balancing resource allocation with risk.

Organizations should immediately upgrade Rebuild installations to version 4.1.4 or later to remediate the vulnerability. In addition to patching, implement robust input validation and output encoding on all user-supplied data, especially in comment and guestbook modules, to prevent injection of malicious scripts. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. Regularly audit web application logs for suspicious comment submissions or unusual user activity indicative of attempted XSS exploitation. Educate users about the risks of clicking unknown links or interacting with untrusted content. Consider deploying web application firewalls (WAFs) with rules tuned to detect and block XSS payloads targeting the affected component. Finally, maintain an up-to-date inventory of Rebuild deployments across the organization to ensure no vulnerable instances remain unpatched.