CVE-2025-24075 is a stack-based buffer overflow vulnerability classified under CWE-121, affecting Microsoft Office Excel within Microsoft 365 Apps for Enterprise version 16.0.1. This vulnerability arises from improper handling of data on the stack, allowing an attacker to overwrite memory and execute arbitrary code. The flaw can be triggered when a user opens a specially crafted Excel file, leading to local code execution without requiring prior authentication or elevated privileges. The attack vector is local (AV:L), with low attack complexity (AC:L), no privileges required (PR:N), but user interaction is necessary (UI:R). The vulnerability impacts confidentiality, integrity, and availability (all rated high), meaning an attacker could fully compromise the affected system. Although no public exploits are known at this time, the vulnerability has been officially published and enriched by CISA, indicating its seriousness. The absence of patches means organizations must rely on mitigations until updates are available. The vulnerability’s exploitation scope is limited to local systems where users open malicious Excel files, but given the widespread use of Microsoft 365 Apps in enterprises, the potential impact is significant. The vulnerability is rated high severity with a CVSS 3.1 score of 7.8, reflecting the risk of full system compromise through user interaction.

For European organizations, this vulnerability poses a significant risk due to the widespread adoption of Microsoft 365 Apps for Enterprise in business, government, and critical infrastructure sectors. Successful exploitation can lead to arbitrary code execution, enabling attackers to steal sensitive data, disrupt operations, or deploy malware such as ransomware. The requirement for local access and user interaction limits remote exploitation but does not eliminate risk, as phishing or social engineering can induce users to open malicious Excel files. Confidentiality breaches could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity and availability impacts could disrupt business continuity, especially in sectors relying heavily on Excel for financial modeling, reporting, or operational planning. The lack of patches increases exposure time, necessitating immediate mitigation. Attackers targeting European entities may leverage this vulnerability to gain footholds in networks, escalate privileges, and move laterally, amplifying the threat landscape.

European organizations should implement the following specific mitigations: 1) Enforce strict email and file filtering policies to block or quarantine Excel files from untrusted or external sources. 2) Disable or restrict macros and ActiveX controls in Excel to reduce attack surface. 3) Educate users about the risks of opening unsolicited or suspicious Excel attachments, emphasizing phishing awareness. 4) Use application control or whitelisting solutions to prevent execution of unauthorized code spawned by Excel processes. 5) Monitor endpoint behavior for anomalies indicative of exploitation attempts, such as unusual process spawning or memory usage. 6) Employ network segmentation to limit lateral movement if a system is compromised. 7) Prepare for rapid deployment of patches once Microsoft releases updates by maintaining an up-to-date asset inventory and patch management process. 8) Consider deploying Microsoft Defender Exploit Guard or similar endpoint protection features that can mitigate exploitation of memory corruption vulnerabilities. These steps go beyond generic advice by focusing on controlling the specific attack vector and limiting impact until a patch is available.