CVE-2025-30379 is a high-severity vulnerability identified in Microsoft Office Online Server version 1.0.0, specifically related to Microsoft Office Excel functionality within the server environment. The vulnerability is classified under CWE-763, which involves the release of an invalid pointer or reference. This type of flaw typically occurs when a program frees or releases a pointer that does not point to a valid object or memory location, potentially leading to memory corruption. In this case, the vulnerability allows an unauthorized attacker to execute arbitrary code locally on the affected system. The CVSS 3.1 base score of 7.8 reflects a high severity level, with the vector indicating that the attack requires local access (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but does require user interaction (UI:R). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the vulnerability poses a significant risk due to the potential for local code execution without authentication. The lack of available patches at the time of publication further increases the urgency for mitigation. The vulnerability could be triggered when a user interacts with a maliciously crafted Excel document or content processed by the Office Online Server, leading to the release of invalid pointers and subsequent execution of attacker-controlled code.

For European organizations, the impact of CVE-2025-30379 can be substantial, especially for enterprises and public sector entities relying on Microsoft Office Online Server to provide collaborative document editing and sharing capabilities. Successful exploitation could lead to full compromise of the server hosting Office Online Server, enabling attackers to execute arbitrary code locally. This could result in unauthorized access to sensitive documents, disruption of business operations, data theft, or lateral movement within the network. Given the high confidentiality, integrity, and availability impacts, organizations could face significant operational downtime, data breaches, and compliance violations under regulations such as GDPR. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, as attackers could leverage social engineering or insider threats to trigger the vulnerability. Additionally, Office Online Server is often integrated with other Microsoft services and enterprise infrastructure, amplifying the potential damage if compromised.

To mitigate CVE-2025-30379 effectively, European organizations should implement the following specific measures: 1) Immediately assess and inventory all deployments of Microsoft Office Online Server version 1.0.0 to identify vulnerable instances. 2) Apply any available patches or updates from Microsoft as soon as they are released; monitor official Microsoft security advisories closely. 3) Restrict local access to Office Online Server hosts to trusted administrators only, employing strict access controls and network segmentation to minimize exposure. 4) Implement application whitelisting and endpoint protection solutions on servers to detect and block unauthorized code execution attempts. 5) Educate users and administrators about the risks of interacting with untrusted or suspicious Excel documents, emphasizing cautious handling of files from unknown sources. 6) Enable detailed logging and monitoring on Office Online Server hosts to detect anomalous activities indicative of exploitation attempts. 7) Consider deploying additional security controls such as Microsoft Defender for Endpoint or equivalent EDR solutions to provide real-time detection and response capabilities. 8) Review and harden the configuration of Office Online Server and underlying operating systems to reduce attack surface and privilege escalation opportunities.