CVE-2026-97776 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 containing specially crafted formulas, embedded objects, or specific formatting structures that trigger incorrect memory allocation calculations during parsing and rendering operations. The root cause lies in insufficient validation of input data lengths against pre-allocated buffer sizes, allowing an attacker to overwrite adjacent memory locations with arbitrary data. This overwriting can corrupt internal application state variables, function return addresses, or exception handling pointers, thereby disrupting the normal flow of execution within the Excel process.
The operational impact of this vulnerability is severe due to its potential for remote code execution without user interaction beyond opening a malicious file. An unauthorized attacker can exploit this flaw by hosting a specially crafted Office document on a web server and convincing a victim to open it via social engineering or automated phishing campaigns. Upon loading the compromised file, Excel processes the malformed data structures, triggering the heap overflow condition. By carefully crafting the payload within the overwritten memory regions, an attacker can inject shellcode that hijacks the execution context of the process running under the privileges of the current user. This allows for full control over the affected system, enabling activities such as installing malware, stealing sensitive credentials, establishing persistence mechanisms, or pivoting to other systems on the network. The ability to execute code remotely makes this a high-severity threat vector often associated with targeted attacks and advanced persistent threats seeking initial access through document-based vectors.
From an industry standards perspective, this vulnerability aligns closely with CWE-122, which defines heap-based buffer overflow as writing data past the end or beginning of a heap allocated buffer. It also relates to CWE-787, regarding out-of-bounds write vulnerabilities in general memory management contexts. In terms of offensive security frameworks like MITRE ATT&CK, this exploitation technique falls under T1203, which covers Exploitation for Client Execution, specifically leveraging client-side applications such as office productivity suites. The attack vector is classified as Network-based because the malicious file can be delivered over remote networks including the internet or internal LANs via email attachments, shared drives, or web downloads.
Mitigation strategies must address both immediate remediation and long-term defense in depth. Organizations should immediately apply the latest security patches released by Microsoft to update Excel and related Office components, as these updates typically include bounds checking improvements and input validation fixes that prevent the overflow condition from occurring. Administrators should enforce strict email filtering policies to block attachments with executable extensions or known malicious file types while implementing sandboxing solutions like Microsoft Defender for Office 365 to analyze documents in isolated environments before delivery to end-users. Additionally, enabling Protected View by default ensures that files downloaded from the internet open in a restricted mode where macros are disabled and editing is prevented until explicitly trusted. User awareness training remains critical to reduce susceptibility to social engineering tactics used to deliver such malicious payloads. Regular vulnerability scanning and patch management cycles should be maintained to ensure timely deployment of fixes for known vulnerabilities in productivity software, minimizing the window of exposure to exploitation attempts.