CVE-2026-97770 in Excel
Summary
by MITRE • 10/15/2026
Stack-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 stack-based buffer overflow condition. This type of memory corruption error occurs when a program writes more data to a fixed-length block of memory on the call stack than it is allocated to hold. In the context of Excel, this typically arises from improper validation or bounds checking of input parameters passed to internal functions that process file formats, macros, or embedded objects. When an attacker crafts a malicious document containing specially formatted content with oversized data fields, they can overwrite adjacent memory locations on the stack. This overwriting often targets critical control structures such as return addresses or function pointers, thereby hijacking the execution flow of the application.
From a technical perspective, this flaw aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-121: Stack-based Buffer Overflow and potentially CWE-787 if it involves out-of-bounds writes affecting critical system structures. The exploitation mechanism relies on the attacker's ability to inject shellcode or other malicious payloads into the memory space controlled by the overflowed buffer. By carefully crafting the payload, an unauthorized actor can achieve arbitrary code execution with the privileges of the currently logged-in user. This is particularly dangerous because it does not require physical access or local authentication; instead, it allows for remote exploitation over a network if the victim opens the malicious file via email attachments, shared drives, or web downloads.
The operational impact of this vulnerability is severe, as successful exploitation grants an attacker full control over the affected system. This can lead to complete data compromise, including theft of sensitive corporate information stored within Excel files or accessible through the compromised user profile. Furthermore, it enables the installation of malware, such as ransomware, keyloggers, or backdoors, facilitating persistent access and lateral movement within a network environment. The attacker may also use this foothold to escalate privileges if additional vulnerabilities are present in the underlying operating system, potentially gaining administrative rights.
In terms of threat actor behavior, this vulnerability is frequently associated with ATT&CK techniques such as T1204: User Execution, where victims are tricked into opening malicious files, and T1059: Command and Scripting Interpreter if the executed code involves scripting languages often found in Excel macros. It also relates to T1068: Exploitation for Privilege Escalation should the attacker leverage this initial access to gain higher-level permissions. The attack vector is primarily network-based, making it a significant risk for organizations that rely heavily on email communication and file sharing services.
Mitigation strategies must focus on both technical controls and user awareness. Organizations should immediately apply all available security patches from Microsoft to update Excel and the underlying Office suite components. Implementing application whitelisting can prevent unauthorized executables from running, even if they are successfully injected via this vulnerability. Additionally, enabling Protected View for files originating from the internet or untrusted locations adds a layer of isolation that prevents automatic execution of potentially harmful content. Users should be trained to recognize suspicious email attachments and avoid opening documents from unknown sources. Network segmentation can also limit the blast radius by restricting lateral movement if an endpoint is compromised. Regular vulnerability scanning and monitoring for anomalous process creation events related to Office applications are essential components of a robust defense-in-depth strategy against such exploits.