CVE-2026-85875 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 an out-of-bounds read flaw within the core processing engine of Microsoft Office Excel, a widely deployed spreadsheet application used across enterprise and consumer environments globally. This specific type of memory safety error occurs when the software attempts to access data at a memory address that lies outside the boundaries of the intended buffer or array structure. In the context of modern operating systems, such as Windows, memory protection mechanisms are designed to prevent processes from accessing arbitrary regions of system memory. However, an out-of-bounds read does not typically allow for code execution but rather facilitates unauthorized information disclosure. When Excel parses a specially crafted file containing malformed data structures or corrupted metadata, it may calculate incorrect offsets due to logic errors in the parsing routine. This miscalculation leads the application to read from adjacent memory locations that contain sensitive operational data, such as stack contents, heap pointers, or other internal state variables of the process.
From a technical perspective, this flaw aligns with Common Weakness Enumeration identifier CWE-125, which defines out-of-bounds read vulnerabilities where software reads past the end of an allocated buffer. The root cause often stems from insufficient validation of input data lengths or indices before they are used to access memory arrays. In Excel's case, complex formulas, embedded objects, or specific cell formatting instructions might trigger edge cases in the rendering engine that fail to properly bound-check array accesses. An attacker who can trick a user into opening a malicious document hosted on a web server or delivered via email can exploit this condition. The exploitation process relies on the victim initiating the action of opening the file, as these vulnerabilities generally require local execution context within the application's sandboxed environment.
The operational impact of this vulnerability is primarily centered around information disclosure rather than remote code execution or system compromise. By leveraging the out-of-bounds read, an attacker can potentially leak portions of Excel’s memory space back to themselves through controlled output mechanisms embedded in the malicious file. This leaked data may include cryptographic keys used for document encryption, session tokens, partial contents of other open documents, or internal pointers that could aid in further exploitation attempts against more complex defenses like Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR). While the immediate risk is limited to local information leakage, such disclosures can serve as a stepping stone for attackers aiming to escalate privileges or bypass security controls within an organization’s network. The attack vector is classified under ATT&CK technique T1059, specifically involving command and script interpreters if combined with other vulnerabilities, but in isolation, it represents a passive data exfiltration method that requires user interaction.
Mitigation strategies for this vulnerability focus on both technical controls and administrative policies to reduce the attack surface. Organizations should ensure that Microsoft Office applications are updated regularly through Windows Update or the Microsoft Security Response Center (MSRC) channels to receive patches addressing these memory safety issues. Additionally, implementing application control solutions such as AppLocker or Windows Defender Application Control can restrict Excel from executing scripts or loading untrusted add-ins, thereby limiting the potential impact of any successful exploitation attempt. Users should be educated on social engineering tactics and advised against opening documents from unknown sources, particularly those with double extensions like .xlsx.exe which may bypass default file extension hiding settings. Furthermore, enabling Protected View for files originating from the internet adds an additional layer of isolation by running Excel in a sandboxed environment where memory access is heavily restricted, preventing the out-of-bounds read data from being fully utilized or exfiltrated to external systems.