CVE-2026-97769 in Excel
Summary
by MITRE • 10/14/2026
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 • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a heap-based buffer overflow condition. 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 arises during the processing of complex or malformed spreadsheet files that contain specially crafted objects, formulas, or embedded content. The application fails to adequately validate the size of incoming data against the pre-allocated memory space before performing copy operations. This lack of rigorous boundary checking allows an attacker to overwrite adjacent memory structures on the heap, which can corrupt internal pointers and control flow mechanisms essential for normal program execution.
From a technical perspective, heap-based buffer overflows are particularly dangerous because they allow attackers to manipulate critical data structures such as function return addresses or exception handling routines. By carefully crafting the overflow payload, an unauthorized actor can gain arbitrary code execution capabilities within the context of the currently logged-in user. Since Excel is frequently used to open documents received via email or downloaded from untrusted sources over a network, this vulnerability presents a significant remote attack vector. An attacker does not necessarily need physical access to the target system; instead, they can distribute malicious files through phishing campaigns or compromised websites that trigger the exploit when the victim opens the document in Excel.
The operational impact of successfully exploiting this heap-based buffer overflow is severe and multifaceted. Once code execution is achieved, an attacker gains full control over the affected application and potentially the underlying operating system depending on user privileges and security configurations like Data Execution Prevention (DEP) or Address Space Layout Randomization (ASLR). This can lead to complete compromise of the target machine, including theft of sensitive corporate data, installation of malware such as ransomware or backdoors, and use of the compromised host as a pivot point for further lateral movement within an enterprise network. The ability to execute code over a network amplifies the risk significantly, making this vulnerability attractive to automated botnets and state-sponsored threat actors seeking widespread initial access.
To mitigate the risks associated with this vulnerability, organizations must prioritize immediate patching of Microsoft Office Excel through official Windows Update channels or standalone security updates provided by Microsoft. Administrators should enforce strict software update policies to ensure all endpoints are running versions that include fixes for known heap overflow conditions in office applications. Additionally, implementing application control solutions such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and binaries, thereby limiting the impact even if an exploit is attempted. Users should be educated on social engineering tactics and advised to exercise caution when opening documents from unknown sources. Enabling Protected View for files originating from the internet adds a layer of isolation by running Excel in a sandboxed environment where potentially malicious code cannot interact with the host system directly.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifiers such as CWE-120, which describes buffer copy without checking size limits, and more specifically CWE-122 for heap-based buffer overflows that lead to memory corruption. In terms of tactical classification under the MITRE ATT&CK framework, this exploit mechanism relates to techniques involving exploitation for remote code execution, often categorized under initial access vectors like spearphishing attachment or drive-by compromise. The reliance on network delivery underscores the importance of robust email filtering and web proxy security controls to intercept malicious payloads before they reach end-user devices. Continuous monitoring for anomalous process creation events related to Excel can also aid in detecting attempted exploitation activities in real-time, allowing incident response teams to contain threats before significant damage occurs.