CVE-2024-30042 is a high-severity vulnerability affecting Microsoft Office Online Server, specifically related to Microsoft Excel functionality. The vulnerability is classified under CWE-502, which involves deserialization of untrusted data. Deserialization vulnerabilities occur when an application deserializes data from an untrusted source without sufficient validation, potentially allowing an attacker to execute arbitrary code. In this case, the flaw allows remote code execution (RCE) when a specially crafted Excel file or data payload is processed by the Office Online Server. The CVSS v3.1 base score is 7.8, indicating a high impact. The attack vector is local (AV:L), meaning the attacker must have local access to the system or network segment where Office Online Server is deployed. No privileges are required (PR:N), but user interaction is necessary (UI:R), implying that the victim must open or interact with malicious content. The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning successful exploitation could lead to full system compromise, data theft, or service disruption. The vulnerability was publicly disclosed on May 14, 2024, with no known exploits in the wild at the time of publication. The affected versions are referenced via Microsoft's security release page, indicating that patches or mitigations may be available or forthcoming. This vulnerability is particularly critical because Office Online Server is often deployed in enterprise environments to provide browser-based access to Office documents, making it a valuable target for attackers seeking to compromise corporate networks through document-based attacks.

For European organizations, the impact of CVE-2024-30042 can be significant. Many enterprises and public sector entities in Europe rely on Microsoft Office Online Server to enable collaborative document editing and remote access to Office files. Exploitation of this vulnerability could allow attackers to execute arbitrary code on the server hosting Office Online Server, potentially leading to full compromise of the server and lateral movement within the network. This could result in data breaches involving sensitive corporate or personal data, disruption of critical business processes, and damage to organizational reputation. Given the high impact on confidentiality, integrity, and availability, organizations could face regulatory consequences under GDPR if personal data is exposed. Additionally, the requirement for user interaction means phishing or social engineering campaigns targeting European users could be used to trigger exploitation, increasing the risk of successful attacks. The lack of known exploits in the wild currently provides a window for proactive mitigation, but the high severity score underscores the urgency for organizations to address this vulnerability promptly.

European organizations should implement the following specific mitigation steps: 1) Immediately review and apply any available security updates or patches from Microsoft for Office Online Server as referenced on the official Microsoft security releases page. 2) Restrict access to Office Online Server to trusted internal networks and VPNs to reduce exposure to local attack vectors. 3) Implement strict network segmentation and monitoring around servers hosting Office Online Server to detect anomalous activity indicative of exploitation attempts. 4) Educate users on the risks of interacting with unsolicited or suspicious Excel files, especially those received via email or external sources, to reduce the likelihood of triggering the vulnerability. 5) Employ application whitelisting and endpoint detection and response (EDR) solutions on servers to prevent or detect unauthorized code execution. 6) Review and harden deserialization handling configurations if customizable within Office Online Server or related infrastructure. 7) Monitor threat intelligence feeds for any emerging exploit code or attack campaigns targeting this vulnerability to enable rapid response. These targeted measures go beyond generic patching advice by focusing on access control, user awareness, and detection capabilities tailored to the nature of this vulnerability.