CVE-2026-81953 in Excel
Summary
by MITRE • 09/09/2026
Stack-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a stack-based buffer overflow. 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 happens during the processing of specific file formats or embedded objects where input validation mechanisms are insufficient. An attacker can craft a malicious document containing specially formatted content that triggers this overflow condition when opened by a victim using the vulnerable version of Microsoft Office Excel. The excessive data overwrites adjacent memory locations on the stack, potentially including critical control flow information such as return addresses and instruction pointers.
From a technical perspective, this flaw aligns with Common Weakness Enumeration (CWE) identifier CWE-121, which describes a stack-based buffer overflow. When the overwritten return address points to attacker-controlled shellcode or existing executable code within the process memory space, it allows for arbitrary code execution. This mechanism is consistent with ATT&CK technique T1059, Command and Scripting Interpreter, as well as T1203, Exploitation for Client Execution, which details how adversaries exploit software vulnerabilities to gain initial access on a target system. The exploitation does not require remote interaction beyond the delivery of the malicious file, making it a local execution vector once the user interacts with the compromised document.
The operational impact of this vulnerability is severe because it grants an unauthorized attacker full control over the affected application and potentially the underlying operating system. Successful exploitation allows the adversary to execute code with the same privileges as the current user. This can lead to complete compromise of the host machine, including the ability to install programs, view, change, or delete data, and create new accounts with full user rights. In enterprise environments where Excel is widely used for business intelligence and reporting, this vulnerability poses a significant risk for phishing campaigns that rely on social engineering to trick employees into opening malicious spreadsheets.
Mitigation strategies primarily involve applying the latest security updates provided by Microsoft, which patch the underlying memory management issues within the application codebase. Organizations should enforce strict email filtering policies to block attachments from unknown sources and implement application whitelisting to prevent unauthorized executables from running even if exploitation occurs. Additionally, enabling macro protection features and disabling automatic content loading can reduce the attack surface. Users must be educated on recognizing suspicious files and avoiding interaction with documents received from untrusted entities until they have been verified through secure channels or sandboxed environments for analysis.