CVE-2025-30376 is a heap-based buffer overflow vulnerability identified in Microsoft Excel, part of Microsoft 365 Apps for Enterprise version 16.0.1. This vulnerability arises from improper handling of memory buffers on the heap, which can be exploited when a user opens a specially crafted Excel file. The flaw allows an attacker to execute arbitrary code locally without requiring prior privileges, but user interaction is necessary to trigger the exploit. The vulnerability impacts confidentiality, integrity, and availability, potentially enabling full system compromise. The CVSS 3.1 score of 7.8 indicates a high-severity issue with an attack vector of local access, low attack complexity, no privileges required, but user interaction is mandatory. No patches were available at the time of publication, and no known exploits were detected in the wild. The vulnerability was reserved in March 2025 and published in May 2025, with enrichment from CISA. The CWE classification is CWE-122 (Heap-based Buffer Overflow), indicating a classic memory corruption issue that can lead to arbitrary code execution. This vulnerability is particularly concerning due to the ubiquity of Microsoft 365 in enterprise environments and the common use of Excel for business-critical tasks.

The impact on European organizations is significant given the widespread adoption of Microsoft 365 Apps for Enterprise across industries such as finance, manufacturing, government, and critical infrastructure. Successful exploitation can lead to local code execution, allowing attackers to escalate privileges, steal sensitive data, disrupt operations, or deploy ransomware. Confidentiality is at risk as attackers could access sensitive spreadsheets and related data. Integrity could be compromised by altering Excel files or injecting malicious macros. Availability may be affected if attackers disrupt Excel or broader system functionality. The requirement for user interaction (opening a malicious file) means phishing or social engineering campaigns could be leveraged. European organizations with high reliance on Excel for data analysis, reporting, and decision-making are particularly vulnerable. The absence of known exploits currently reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits rapidly after disclosure.

Organizations should prioritize deploying security updates from Microsoft as soon as patches become available for this vulnerability. Until patches are released, implement strict controls on email attachments and file downloads, especially Excel files from untrusted sources. Employ advanced endpoint detection and response (EDR) solutions capable of detecting anomalous behavior related to memory corruption exploits. Use application whitelisting and restrict macro execution within Excel to reduce attack surface. Conduct user awareness training focused on phishing and social engineering risks to minimize the chance of malicious file execution. Network segmentation can limit lateral movement if exploitation occurs. Additionally, monitor logs for unusual Excel process activity and consider deploying sandboxing solutions to analyze suspicious Excel files before allowing user access. Regularly back up critical data to enable recovery in case of compromise.