CVE-2026-97777 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 inputs without adequate bounds checking, it overwrites adjacent memory locations on the heap. This overwrite can corrupt internal data structures used by the application, such as function pointers or object headers, which are critical for normal program execution flow.
The operational impact of this vulnerability is severe due to its potential for remote code execution. Because Microsoft Office applications are frequently used to open documents received via email attachments or downloaded from untrusted sources over a network, an attacker can exploit this flaw by distributing a malicious file designed to trigger the overflow condition. Upon opening such a file, the application may crash immediately, causing denial of service, but more dangerously, it allows for arbitrary code execution under the context of the currently logged-in user. This means that if a victim opens the crafted document, an attacker can execute commands with the same privileges as the user, potentially leading to full system compromise, installation of malware, data theft, or lateral movement within a corporate network environment.
From a technical classification perspective, this vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write in the heap space. These classifications highlight the fundamental failure in input validation and memory management practices within the software component responsible for parsing Excel file formats. The lack of rigorous boundary checks during the processing of specific data structures allows external inputs to dictate internal program behavior, violating the principle of least privilege and safe memory handling expected in enterprise-grade productivity software.
In terms of adversary tactics, this exploitation vector is consistent with techniques observed in the MITRE ATT&CK framework, particularly those related to Initial Access via Spearphishing Attachment or Drive-by Compromise through Malicious Files. Attackers often leverage social engineering to persuade users into opening seemingly legitimate documents that contain hidden malicious payloads triggering such memory corruption bugs. The ability to execute code over a network underscores the urgency of addressing this flaw, as it transforms a local application bug into a widespread remote attack surface accessible across organizational boundaries without requiring physical access or prior authentication beyond user interaction with the file.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. The primary defense is to apply the latest security updates provided by Microsoft for all affected versions of Office Excel, which include patches designed to enforce stricter memory management protocols and input validation checks. Organizations should also implement application whitelisting policies to prevent unauthorized or untrusted scripts from executing within office applications, thereby limiting the impact even if a vulnerability is exploited. Additionally, deploying advanced email security gateways that inspect attachments for malicious patterns can reduce exposure. User awareness training remains critical, emphasizing caution when opening files from unknown sources, as technical controls alone cannot eliminate all risks associated with social engineering and zero-day exploits until patches are universally deployed.