CVE-2026-81400 in Excel
Summary
by MITRE • 09/09/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to disclose information 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 categorized as an out-of-bounds read error. This type of memory corruption issue arises when the software attempts to access data stored at a memory location that is outside the boundaries of the intended buffer or array structure. In the context of Excel, this typically occurs during the parsing and rendering of complex spreadsheet files, particularly those containing malformed formulas, embedded objects, or specially crafted binary structures designed to exploit specific edge cases in the application's internal logic. The root cause lies in insufficient validation checks performed by the parser before accessing memory addresses derived from user-supplied input within the document file.
From a technical perspective, an out-of-bounds read differs significantly from an out-of-bounds write in that it does not allow for arbitrary code execution or direct modification of system state through overwriting data structures. Instead, the primary consequence is the unauthorized disclosure of sensitive information residing in adjacent memory locations. When Excel processes a maliciously crafted file, the flawed logic causes the application to read memory contents beyond the allocated buffer and return these values to the user interface or internal processing routines. This can result in the leakage of stack data, heap metadata, or other confidential information that was previously stored in nearby memory regions. Such leaks are particularly dangerous because they can provide attackers with valuable intelligence about the target environment, including version numbers, loaded modules, and potentially cryptographic keys if present in adjacent memory spaces.
The operational impact of this vulnerability is primarily centered on confidentiality rather than integrity or availability. An unauthorized attacker who successfully exploits this flaw can disclose local information from the victim's machine without requiring elevated privileges. This capability aligns with Common Weakness Enumeration (CWE) category CWE-125, which defines out-of-bounds read as a weakness where software reads data past the end of a buffer or array. In terms of offensive security frameworks, this behavior maps to MITRE ATT&CK technique T1005, Data from Local System, specifically under sub-techniques related to application crash dumping or memory scraping. The attacker leverages the vulnerability as an initial vector for information gathering, which can subsequently facilitate more advanced attacks such as privilege escalation or lateral movement within a networked environment by identifying vulnerable services or exposed credentials.
Mitigation strategies for this vulnerability rely heavily on timely patching and defensive configuration practices. Microsoft has addressed these issues through cumulative security updates that correct the memory access validation logic within Excel's parsing engine. Organizations must ensure that all endpoints running affected versions of Office are updated to the latest stable release containing the relevant hotfixes. Additionally, implementing application control policies can restrict the execution of untrusted scripts or macros, thereby reducing the attack surface for drive-by exploitation scenarios where users might inadvertently open malicious documents. Network segmentation and endpoint detection and response (EDR) solutions should also be configured to monitor for anomalous memory access patterns that may indicate an active exploit attempt in progress.