CVE-2026-97766 in Office
Summary
by MITRE • 10/15/2026
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a heap-based buffer overflow. This type of memory corruption error occurs when a program writes data beyond the allocated boundaries of a buffer located in the heap segment of computer memory. In the context of Excel, this typically involves the processing of complex or malformed spreadsheet files that contain specially crafted formulas, embedded objects, or structured storage elements designed to exploit parsing logic errors. When an attacker crafts a malicious document with specific input parameters exceeding expected limits, they can overwrite adjacent memory structures on the heap, potentially gaining control over critical data pointers such as function return addresses or exception handlers. This manipulation allows for arbitrary code execution under the context of the currently logged-in user, effectively bypassing standard security controls and granting the attacker full administrative privileges if the victim operates with elevated rights.
From a technical perspective, this vulnerability aligns closely with Common Weakness Enumeration identifier CWE-120, which classifies buffer copies without checking size limits. The exploitation mechanism relies on precise memory layout manipulation to achieve code execution rather than simple denial of service. Attackers often leverage social engineering tactics to deliver the malicious file via email attachments or network shares, capitalizing on the fact that Excel is a widely used productivity tool with deep system integration. Once opened, the application processes the malformed input during its parsing phase, triggering the overflow condition before any user interaction beyond opening the document is required in many scenarios. This characteristic makes it particularly dangerous as remote code execution can occur without further user action after the initial file open event.
The operational impact of this vulnerability extends far beyond simple data corruption or application crashes. Successful exploitation enables an unauthorized attacker to execute arbitrary commands on the target system, which may include downloading and installing additional malware, creating new user accounts with administrative privileges, stealing sensitive credentials stored in memory or on disk, and pivoting to other systems within the internal network. This significantly compromises the confidentiality, integrity, and availability of organizational assets. In enterprise environments where Excel is a primary tool for data analysis and reporting, such vulnerabilities pose a severe risk to business continuity and regulatory compliance, particularly in sectors governed by strict data protection standards like GDPR or HIPAA.
To mitigate this threat, organizations must prioritize immediate patching through Microsoft Update services to ensure all instances of Office Excel are updated with the latest security fixes addressing heap overflow conditions. Administrators should also implement application whitelisting policies using tools such as AppLocker or Windows Defender Application Control to restrict the execution of untrusted scripts and binaries from temporary folders where malicious documents might be saved by default browsers or email clients. Network segmentation can further limit lateral movement if an endpoint is compromised, while user awareness training remains essential to prevent social engineering attacks that deliver these exploit vectors. Additionally, enabling Protected View for files originating from the internet forces Excel to open such documents in a sandboxed environment with restricted permissions, thereby neutralizing many exploitation attempts before they reach the core application logic. These measures collectively reduce the attack surface and provide defense-in-depth against heap-based memory corruption vulnerabilities like this one.