CVE-2026-81395 in 365 Apps for Enterprise
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 an out-of-bounds read flaw within the core processing engine of Microsoft Office Excel, a widely deployed spreadsheet application integral to enterprise and personal computing environments. This specific class of memory safety error occurs when the software attempts to access data at a memory address that lies outside the intended buffer boundary. In this context, rather than writing malicious data which could lead to code execution, the flaw allows for reading sensitive information from adjacent memory locations. The root cause typically stems from insufficient validation checks on array indices or pointer arithmetic during the parsing of complex Excel files, particularly those containing intricate formulas, macros, or specially crafted binary structures that exploit edge cases in the rendering and calculation engines.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-125, which defines out-of-bounds read as accessing memory beyond the allocated buffer limits. When an attacker crafts a malicious Excel file designed to trigger this condition, they can manipulate the application's state such that it leaks contents of adjacent heap or stack segments back into the output stream or visible interface elements. This mechanism facilitates local information disclosure, allowing an unauthorized actor who has successfully tricked a user into opening the document to extract sensitive data residing in the process memory space. The attack vector is primarily social engineering based, requiring initial interaction with the malicious file, which places it within the MITRE ATT&CK framework under techniques related to Initial Access and potentially Data from Local System depending on what specific information is exfiltrated.
The operational impact of this vulnerability centers on confidentiality rather than integrity or availability. While out-of-bounds reads are often considered less severe than buffer overflows that permit arbitrary code execution, they remain critical in scenarios where the leaked data includes cryptographic keys, session tokens, passwords stored in memory by other applications, or proprietary business logic embedded within complex spreadsheets. For organizations relying on Excel for sensitive financial modeling or confidential reporting, such a leak can lead to significant intellectual property theft and compliance violations under regulations like GDPR or HIPAA if personal identifiable information is exposed. The risk is amplified by the ubiquity of Microsoft Office across corporate networks, making it a high-value target for threat actors seeking low-effort initial footholds that yield immediate intelligence gains.
Mitigation strategies must address both technical controls and user awareness to effectively reduce exposure. Immediate remediation involves applying the latest security patches released by Microsoft through Windows Update or the standalone update catalog, as these updates contain code fixes that enforce stricter bounds checking during file parsing operations. Administrators should prioritize patching workstations where Excel is heavily utilized for handling external documents. Additionally, implementing application control policies such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and macros often associated with exploiting this vulnerability. User training remains crucial; employees must be educated to recognize suspicious file origins and avoid opening attachments from unknown senders. Enabling Protected View by default for files originating from the internet adds a sandboxed layer that prevents active content from executing until explicitly trusted, thereby neutralizing many exploitation attempts before they can interact with vulnerable memory structures.