CVE-2025-11276 is a cross-site scripting (XSS) vulnerability identified in the Rebuild software product, specifically affecting versions 4.1.0 through 4.1.3. The vulnerability resides in an unspecified functionality within the Comment/Guestbook component of Rebuild. An attacker can exploit this flaw remotely by manipulating input fields related to comments or guestbook entries, injecting malicious scripts that execute in the context of the victim's browser. This type of vulnerability enables attackers to perform actions such as session hijacking, defacement, or redirecting users to malicious sites. The vulnerability does not require authentication but does require user interaction (e.g., a victim visiting a crafted page or comment). The vendor has acknowledged the issue and released a fix in version 4.1.4. The CVSS v4.0 base score is 5.1, indicating a medium severity level, with characteristics including network attack vector, low attack complexity, no privileges required, but user interaction needed. The vulnerability impacts confidentiality and integrity to a limited extent, with no direct impact on availability. No known exploits are currently reported in the wild. The flaw was published on October 5, 2025, and the vendor's fix is recommended to mitigate the risk.

For European organizations using Rebuild versions 4.1.0 to 4.1.3, this vulnerability poses a moderate risk. Since the flaw allows remote attackers to inject malicious scripts into comment or guestbook functionalities, it could lead to session hijacking, theft of sensitive user data, or distribution of malware through trusted websites. Organizations relying on Rebuild for public-facing websites or community engagement platforms may face reputational damage, loss of user trust, and potential regulatory scrutiny under GDPR if personal data is compromised. The impact is more pronounced for entities with high user interaction on affected components. However, the lack of requirement for elevated privileges and the need for user interaction somewhat limit the scope of exploitation. Nonetheless, attackers could leverage social engineering or automated scripts to increase attack success. The vulnerability does not affect system availability directly but can undermine data integrity and confidentiality, which are critical for compliance and operational security in European contexts.

European organizations should immediately upgrade Rebuild installations to version 4.1.4 or later, as this version contains the vendor-provided patch addressing the XSS vulnerability. Additionally, organizations should implement input validation and output encoding on all user-supplied content in the Comment/Guestbook components to prevent script injection. Employing Content Security Policy (CSP) headers can further mitigate the impact of any residual XSS risks by restricting script execution sources. Web Application Firewalls (WAFs) configured to detect and block XSS payloads can provide an additional layer of defense. Regular security audits and penetration testing focusing on user input handling should be conducted to identify any other potential injection points. Finally, educating users about the risks of interacting with untrusted content can reduce the likelihood of successful exploitation.