CVE-2026-81399
Summary
by MITRE • 09/08/2026
Buffer over-read in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described constitutes a buffer over-read flaw within the core processing engine of Microsoft Office Excel, specifically affecting how the application handles certain data structures or file formats during parsing operations. This type of memory safety issue arises when the software attempts to read from a memory location beyond the boundaries of an allocated buffer without performing adequate bounds checking. In the context of enterprise environments where Excel is ubiquitously used for financial modeling and data analysis, this flaw presents a significant risk vector because it can be triggered by opening specially crafted spreadsheet files or documents containing malformed embedded objects. The primary consequence of such a vulnerability is the unauthorized disclosure of sensitive information stored in adjacent memory regions. An attacker who successfully exploits this condition could potentially extract portions of the process memory space that contain private keys, authentication tokens, passwords, or other confidential data belonging to the user running the application. This local privilege escalation through information leakage undermines the confidentiality guarantees expected from standard office productivity suites and can serve as a precursor for more severe attacks if combined with additional exploitation techniques such as heap spraying or use-after-free conditions.
From a technical perspective, this flaw aligns closely with Common Weakness Enumeration category CWE-125, which defines out-of-bounds read vulnerabilities where software reads data past the end of a buffer. The operational impact is primarily focused on confidentiality rather than integrity or availability in its initial state, although persistent memory corruption could lead to instability or crashes affecting service availability. Security researchers and threat intelligence platforms often map such local information disclosure vectors to MITRE ATT&CK techniques related to Credential Access, specifically those involving direct system access through application exploitation. The attack vector is typically classified as Local because it requires the victim to open a malicious file, which may be delivered via phishing emails or compromised shared drives. Mitigation strategies must therefore emphasize both technical controls and user awareness. Organizations should ensure that Microsoft Office applications are kept up-to-date with the latest security patches released by Microsoft, as these updates often include rigorous input validation and memory management improvements designed to prevent out-of-bounds access. Additionally implementing application control policies such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts or macros within Excel environments. Users should be trained to exercise caution when opening files from unknown sources and to disable automatic macro execution by default, thereby reducing the attack surface available for triggering this vulnerability through automated processing mechanisms.