CVE-2026-88145 in Office
Summary
by MITRE • 10/14/2026
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 • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a heap-based buffer overflow condition. 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, objects, or embedded content that triggers an incorrect calculation of buffer size during parsing operations. When such input is processed, the application fails to properly validate the length of the data before copying it into a pre-allocated memory region, resulting in adjacent memory being overwritten with attacker-controlled values. This overwriting can corrupt internal data structures used by Excel for managing file states and object references, thereby destabilizing the execution environment.
From an operational perspective, this vulnerability allows for remote code execution without requiring user interaction beyond opening or viewing a malicious document, depending on the specific configuration of trust settings within Microsoft Office. An unauthorized attacker can exploit this flaw over a network by distributing a crafted Excel file through various vectors such as email attachments, shared drives, or web-based downloads. Upon successful exploitation, the attacker gains the ability to execute arbitrary code with the same privileges as the current user. This level of access enables a wide range of malicious activities including data theft, installation of backdoors, deployment of ransomware, and further lateral movement within an enterprise network. The severity is compounded by the ubiquity of Excel in corporate environments and the frequent exchange of spreadsheet files across organizational boundaries.
In terms of industry standard classifications, this vulnerability aligns with Common Weakness Enumeration identifier CWE-120, which denotes Buffer Copy without Checking Size of Input Classic Heap-based Overflow. This classification highlights the fundamental failure to perform bounds checking on input data before memory allocation and copy operations. Furthermore, from a tactical standpoint within the MITRE ATT&CK framework, this vulnerability facilitates initial access via spearphishing attachment or drive-by compromise techniques. The exploitation chain often involves social engineering tactics to trick users into opening malicious documents, followed by code execution that may leverage additional vulnerabilities for privilege escalation if the user operates with elevated permissions.
Mitigation strategies must focus on both technical controls and administrative policies. Organizations should ensure that Microsoft Office applications are updated to the latest versions containing security patches addressing this specific heap overflow issue. Implementing application control solutions such as Windows Defender Application Control or AppLocker can restrict the execution of untrusted scripts and binaries, thereby limiting the impact if exploitation occurs. Additionally, enabling Protected View for files originating from potentially unsafe locations forces Excel to open documents in a sandboxed environment where macros are disabled and interactions with system resources are restricted. Network segmentation and strict email filtering policies that inspect attachments for malicious content also serve as effective defensive layers against this threat vector. Regular vulnerability assessments and penetration testing can help identify instances of unpatched software within the infrastructure, ensuring timely remediation before exploitation attempts materialize in targeted attacks.