CVE-2026-81392 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 that handles complex data structures and formula calculations. This specific class of error occurs when the software attempts to access memory locations beyond the boundaries of allocated buffers during the parsing or rendering of maliciously crafted files. Such flaws are typically rooted in improper validation checks before array indexing operations, allowing an attacker who has successfully delivered a specially constructed Excel file to trigger unauthorized memory reads. The primary consequence of this defect is the local disclosure of sensitive information residing in the process memory space, which may include credentials, encryption keys, or other proprietary data that was previously loaded into the application context but not intended for external exposure.
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 end of an allocated buffer without triggering standard protection mechanisms like segmentation faults in all scenarios. In modern operating systems with advanced memory protections such as Data Execution Prevention and Address Space Layout Randomization, these reads might not always result in immediate code execution but can still leak critical data through side-channel effects or direct memory dumps if the attacker can control the read length and offset precisely. The exploitation vector generally requires social engineering to persuade a user to open a malicious document, placing this threat within the context of ATT&CK technique T1059, Command and Scripting Interpreter, specifically when combined with subsequent data exfiltration steps that leverage the leaked information for further lateral movement or privilege escalation on the compromised host.
The operational impact of such vulnerabilities extends beyond simple data leakage, as it can serve as a precursor to more severe attacks if additional memory corruption flaws are present in the same component chain. Even in isolation, however, the ability to read arbitrary memory addresses undermines the confidentiality guarantees provided by the operating system and application sandboxing mechanisms. For organizations relying on Excel for critical business operations, this represents a significant risk vector that could lead to intellectual property theft or compromise of authentication tokens stored within browser processes if cross-process data sharing is enabled. Mitigation strategies must prioritize immediate patching through Microsoft Security Update channels to ensure all instances of the affected Office versions are updated with the latest security fixes designed to enforce stricter bounds checking during file parsing routines.
Administrators should also implement application control policies such as AppLocker or Windows Defender Application Control to restrict the execution of untrusted scripts and macros that often accompany these exploit attempts, thereby reducing the attack surface even if a vulnerability is present. Additionally, enabling Protected View for files originating from potentially unsafe locations can isolate the document processing in a sandboxed environment with limited permissions, preventing direct access to sensitive system resources. Regular security awareness training remains essential as technical controls alone cannot fully mitigate risks associated with user interaction and file handling practices that facilitate initial delivery of malicious artifacts targeting known software vulnerabilities like this one.