CVE-2026-97773 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 that contain specially crafted objects, formulas, or embedded content. When the application attempts to parse these malicious inputs, it fails to adequately validate the size of the incoming data against the pre-allocated buffer space. Consequently, excess data overwrites adjacent memory locations on the heap, corrupting internal data structures and control flow mechanisms such as function return addresses or pointer values. This corruption allows an attacker to manipulate the execution context of the application with arbitrary precision.
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 Excel document on a web server or distributing it via email attachments and instant messaging platforms. When a victim opens the compromised file, the overflow condition triggers during the parsing phase, enabling the injection and subsequent execution of arbitrary code within the security context of the current user. This grants the attacker full control over the affected system, facilitating activities such as data theft, installation of malware, creation of backdoors, or pivoting to other systems on the network. The risk is particularly acute in enterprise environments where users frequently open documents from external sources, making this a prime vector for targeted attacks and widespread compromise through social engineering tactics.
From a classification perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-120, which denotes Buffer Copy without Checking Size of Input Classic Heap-based Overflow. This categorization highlights the fundamental failure in input validation that allows data to exceed buffer limits. Furthermore, the exploitation technique maps directly to MITRE ATT&CK techniques related to Initial Access and Execution. Specifically, it corresponds to T1566.002, which involves Phishing: Spearphishing Attachment, as attackers typically deliver such exploits via deceptive emails containing malicious Office documents. The execution phase aligns with T1204.002, User Execution: Malicious File, where the victim's action of opening the file triggers the payload. Understanding these mappings is crucial for defenders to implement appropriate detection rules and behavioral monitoring strategies that identify anomalous process creation or memory manipulation patterns associated with Office applications.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense is the prompt application of security updates provided by Microsoft, which patch the underlying code flaws responsible for the insufficient input validation. Organizations should enforce strict policies regarding the opening of files from untrusted sources and utilize Application Control technologies to restrict the execution of unsigned scripts or macros within Office applications. Additionally, enabling Protected View in Excel ensures that documents opened from potentially unsafe locations are loaded in a sandboxed environment with limited permissions, preventing direct interaction with system resources until explicitly trusted by the user. Network-level defenses such as next-generation firewalls and intrusion prevention systems should be configured to inspect traffic for known exploit signatures associated with this vulnerability. Regular security awareness training is also essential to reduce the likelihood of users falling victim to social engineering campaigns designed to deliver these malicious documents.