CVE-2025-30393 is a high-severity use-after-free vulnerability identified in Microsoft 365 Apps for Enterprise, specifically affecting Microsoft Office Excel version 16.0.1. The vulnerability is classified under CWE-416, which pertains to use-after-free errors where a program continues to use memory after it has been freed, leading to undefined behavior. In this case, an unauthorized attacker can exploit this flaw to execute arbitrary code locally on the affected system. The vulnerability requires local access (Attack Vector: Local), minimal attack complexity (AC:L), no privileges required (PR:N), but user interaction is necessary (UI:R), such as opening a malicious Excel file. The scope is unchanged (S:U), but 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 disruption. Although no known exploits are currently in the wild, the vulnerability's characteristics make it a significant risk, especially in environments where users frequently open Excel documents from untrusted sources. The lack of available patches at the time of publication increases the urgency for mitigation. The vulnerability was reserved in March 2025 and published in May 2025, indicating recent discovery and disclosure.

For European organizations, the impact of CVE-2025-30393 can be substantial. Microsoft 365 Apps for Enterprise, including Excel, is widely used across Europe in both private and public sectors, including critical infrastructure, financial institutions, healthcare, and government agencies. Exploitation could lead to unauthorized code execution on user machines, potentially allowing attackers to escalate privileges, move laterally within networks, exfiltrate sensitive data, or disrupt operations. Given the high confidentiality, integrity, and availability impacts, organizations could face data breaches, operational downtime, regulatory penalties under GDPR, and reputational damage. The requirement for user interaction means phishing or social engineering campaigns could be leveraged to deliver malicious Excel files, a common attack vector in Europe. The absence of known exploits currently provides a window for proactive defense, but the vulnerability's nature suggests it could be weaponized rapidly once exploit code becomes available.

European organizations should implement targeted mitigations beyond generic advice: 1) Enforce strict email filtering and attachment scanning policies to block or quarantine suspicious Excel files, especially from external or unknown senders. 2) Educate users about the risks of opening unsolicited or unexpected Excel documents and train them to recognize phishing attempts. 3) Employ application control or whitelisting solutions to restrict execution of untrusted macros or code within Excel. 4) Utilize endpoint detection and response (EDR) tools to monitor for anomalous behaviors indicative of exploitation attempts, such as unusual memory operations or process injections. 5) Segment networks to limit lateral movement if a local compromise occurs. 6) Monitor Microsoft’s security advisories closely for the release of patches and apply them promptly once available. 7) Consider disabling or restricting features in Excel that are not essential but could be exploited, such as embedded scripting or external content loading. 8) Implement least privilege principles on user accounts to reduce potential impact of local code execution.