CVE-2026-81388 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 involves processing specially crafted files or inputs that contain malformed data structures exceeding expected boundaries. When such an input is processed by the application's parsing engine, the excess data overwrites adjacent memory locations on the stack, which may include critical control information such as return addresses and saved frame pointers. This corruption allows for a complete loss of control flow within the executing process, enabling an attacker to redirect execution to arbitrary code injected into the vulnerable buffer or other accessible memory regions.
From a technical perspective, this flaw aligns with Common Weakness Enumeration identifier CWE-121, which defines stack-based buffer overflow as a condition where data is written beyond the allocated space on the call stack. The operational impact of such a vulnerability is severe, as it permits an unauthorized attacker to execute arbitrary code locally within the context of the currently logged-in user. This capability effectively grants full control over the affected system if the application runs with elevated privileges or if the user has administrative rights. Attackers can leverage this condition to install malware, steal sensitive information, modify data, or create new accounts with unrestricted access. The exploitability often relies on social engineering tactics where a victim is tricked into opening a maliciously crafted Excel file that triggers the overflow during its parsing phase.
In terms of threat modeling and adversary behavior, this vulnerability maps directly to MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution. This tactic involves attackers using software vulnerabilities in client applications like office suites to gain an initial foothold on a target system. The attack vector is typically remote via email or file sharing services, but the execution occurs locally once the user interacts with the malicious document. Defenders must recognize that stack-based overflows are among the most dangerous classes of memory corruption bugs because they provide direct code execution capabilities without requiring additional privilege escalation steps if the application runs with sufficient permissions.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided security patches and updates to ensure that Excel is running a version where the buffer handling logic has been corrected to validate input lengths before copying data to the stack. Organizations should enforce strict policies regarding macro execution and disable unnecessary features in Office applications to reduce the attack surface. Additionally, deploying application whitelisting solutions can prevent unauthorized or untrusted scripts from executing even if they are delivered via a compromised document. Users must be educated on recognizing suspicious file attachments and avoiding opening documents from unknown sources. Regular vulnerability scanning and patch management cycles are essential to ensure that known flaws like this stack-based buffer overflow are remediated promptly, thereby maintaining the integrity and confidentiality of enterprise systems against exploitation attempts.