Excel Under Siege: Analyzing CVE-2025-30376 Heap-Based Buffer Overflow

Introduction

Microsoft Excel, a cornerstone of productivity software, faces a critical security threat with CVE-2025-30376—a heap-based buffer overflow vulnerability. This flaw, rated high severity with a CVSS score of 7.8, allows local attackers to execute arbitrary code simply by tricking users into opening a maliciously crafted Excel file.

Affected Systems and Versions

The following Microsoft Excel versions are specifically vulnerable:

Microsoft Excel 2016 (all updates prior to May 13, 2025)
Microsoft Office 2019
Microsoft Office 2021
Microsoft 365 Apps (Click-to-Run)

Technical Information

CVE-2025-30376 exploits a heap-based buffer overflow vulnerability (CWE-122, CWE-125) in Excel's memory management. The root cause is improper bounds checking during the parsing of Excel files, allowing attackers to write beyond allocated memory boundaries. This memory corruption can lead to arbitrary code execution with the privileges of the currently logged-in user.

Attack Vector and Exploitation Method

The attack vector is local, requiring the victim to open a malicious Excel document. Once opened, the crafted document triggers uncontrolled memory writes, corrupting adjacent heap memory structures. This corruption enables attackers to hijack control flow and execute malicious code.

Patch Information

Microsoft has provided patches addressing CVE-2025-30376 in their May 2025 security updates:

Office 2016: Update to KB5002695
Excel 2016: Update to KB5002717

Patches can be downloaded directly from Microsoft's official update channels:

Microsoft Security Update Guide

Detection Methods

Security teams should monitor for unusual Excel process behaviors, such as spawning unexpected child processes (e.g., cmd.exe, powershell.exe). Additionally, audit Excel files with abnormal metadata or mismatched file extensions. Employing endpoint detection and response (EDR) solutions can help identify exploitation attempts.

Vendor Security History

Microsoft frequently addresses memory corruption vulnerabilities in its Office suite. The May 2025 Patch Tuesday alone fixed 12 Excel-specific vulnerabilities, indicating ongoing challenges in securing legacy codebases. Microsoft's rapid response and regular patch cycles demonstrate a mature security posture, yet the recurrence of similar vulnerabilities highlights persistent risks.

References

Organizations must prioritize patching and adopt comprehensive security measures to mitigate the risks posed by CVE-2025-30376.