CVE-2025-30191 is a vulnerability identified in the Open-Xchange GmbH OX App Suite, a widely used collaboration and email platform. The issue arises from improper restriction of rendered UI layers or frames, specifically allowing malicious content embedded in emails to perform a redressing attack (also known as clickjacking). This attack manipulates the user interface by overlaying or disguising UI elements, tricking users into executing unintended actions or divulging sensitive data to attackers. The root cause was insufficient sanitization of attribute values that could contain HTML fragments, enabling attackers to craft emails that exploit this flaw. The vendor has addressed this by enhancing the sanitization process to deny such HTML fragments in attribute values, reducing the attack surface. The vulnerability requires no privileges to exploit but does require user interaction, such as clicking on a malicious email link or UI element. The CVSS v3.1 base score is 5.4, indicating a medium severity, with attack vector network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), and impacts on confidentiality and integrity but not availability. No public exploits have been reported yet, but the potential for phishing and social engineering attacks leveraging this vulnerability remains significant.

For European organizations, this vulnerability poses a risk primarily to confidentiality and integrity of user data and actions within the OX App Suite environment. Attackers could use crafted emails to trick users into revealing sensitive information, such as credentials or personal data, or to perform unauthorized actions that could lead to further compromise. Sectors with high reliance on email communication and collaboration tools—such as finance, government, healthcare, and critical infrastructure—are particularly vulnerable. The attack does not impact system availability directly but can facilitate broader attacks through social engineering. Given the widespread use of OX App Suite in Europe, especially in Germany and neighboring countries, the potential impact includes data breaches, unauthorized access, and erosion of user trust. The lack of public exploits currently limits immediate risk, but the medium severity score and ease of exploitation via user interaction warrant proactive measures.

Organizations should prioritize applying any official patches or updates released by Open-Xchange GmbH that address this vulnerability. In the absence of immediate patches, administrators should implement enhanced email filtering to detect and quarantine suspicious emails containing potentially malicious HTML content. User awareness training is critical to educate users about the risks of interacting with unexpected or suspicious emails and the signs of redressing or clickjacking attacks. Additionally, deploying Content Security Policy (CSP) headers and frame-busting techniques can help mitigate UI redressing risks by restricting how content is embedded or framed. Monitoring email traffic for anomalies and employing multi-factor authentication (MFA) can reduce the impact of credential theft resulting from this vulnerability. Regular security assessments of the OX App Suite deployment and prompt incident response planning will further strengthen defenses.