CVE-2026-97746 in 365 Apps for Enterprise
Summary
by MITRE • 10/14/2026
Integer underflow (wrap or wraparound) in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves a critical integer underflow flaw within the core processing logic of Microsoft Office Excel, specifically affecting how certain data structures handle numerical values during parsing and rendering operations. This type of defect typically arises when a calculation results in a value lower than the minimum limit for the specific integer type being used, causing the system to wrap around to a large positive number rather than handling the error gracefully or throwing an exception. In the context of Excel files, this often occurs within complex formulas, embedded objects, or specialized data formats where memory allocation is dynamically determined based on user-supplied input values derived from the document structure itself.
From a technical perspective, the underflow allows an attacker to manipulate internal pointers or buffer sizes by supplying crafted numerical inputs that trigger the wraparound condition. When Excel processes these malformed inputs, it may allocate insufficient memory for subsequent operations while simultaneously attempting to write data beyond the bounds of the allocated buffer. This discrepancy creates a classic heap-based buffer overflow scenario, where arbitrary code execution becomes possible if an attacker can control the content written into the overflown region. The exploitability is heightened because Excel frequently processes untrusted documents received via email or downloaded from websites, providing multiple vectors for remote exploitation without requiring physical access to the target machine.
The operational impact of this vulnerability is severe, as it enables unauthorized attackers to execute arbitrary code on a victim's system with the privileges of the currently logged-in user. This can lead to full system compromise, including the installation of malware, theft of sensitive data, or use of the compromised host as part of a botnet. Since Microsoft Office applications are ubiquitous in enterprise environments and often run with elevated permissions due to integration with other corporate tools, the blast radius of such an exploit is significant. Attackers can leverage this flaw for targeted spear-phishing campaigns where malicious Excel files serve as the initial delivery mechanism, bypassing perimeter defenses that may not inspect deep packet contents or macro-enabled documents thoroughly enough.
Mitigation strategies must focus on both immediate remediation and long-term defense-in-depth practices. The primary corrective action is to apply the latest security updates provided by Microsoft, which patch the underlying logic errors responsible for the integer underflow. Organizations should enforce strict policies regarding the opening of Office files from untrusted sources, utilizing application whitelisting or macro blocking features inherent in modern versions of Excel to prevent automatic execution of potentially malicious scripts. Additionally, deploying endpoint detection and response solutions that monitor for anomalous memory allocation patterns can help identify exploitation attempts in real-time. Regular vulnerability assessments and penetration testing should also be conducted to ensure that similar logic flaws are identified before they can be weaponized by threat actors.
This flaw aligns with Common Weakness Enumeration identifier CWE-192, which defines integer underflow or wraparound as a software error resulting from the conversion of an integer value to another type where the original value is too small for the new type. In terms of attack behavior, it falls under MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques such as PowerShell or Windows Command Shell abuse, which are commonly used post-exploitation stages following successful code execution via document-based vulnerabilities like this one. Understanding these classifications helps security teams prioritize patching efforts and configure detection rules that target the specific behavioral indicators associated with exploiting integer arithmetic errors in productivity software.