CVE-2026-78518 in Office
Summary
by MITRE • 09/09/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
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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 involving an out-of-bounds memory read operation. This type of defect typically arises when software accesses data at a memory address that lies outside the intended buffer boundary, either before or after the allocated space for that buffer. In the context of Excel, this error is often triggered by processing specially crafted files containing malformed formulas, embedded objects, or complex formatting structures. When the application attempts to parse these malicious inputs, it fails to adequately validate the length and bounds of the data being processed, leading to a read operation that retrieves unintended memory contents. This behavior aligns with Common Weakness Enumeration category CWE-125, which defines out-of-bounds read vulnerabilities as conditions where software reads past the end or before the beginning of the intended buffer.
The operational impact of this vulnerability is severe due to its potential for remote code execution over a network. An attacker can exploit this flaw by hosting a malicious Excel file on a website or embedding it in an email attachment, thereby leveraging social engineering tactics such as phishing to trick users into opening the document. Once opened, the malformed data triggers the out-of-bounds read, which may allow the attacker to leak sensitive information from memory or, more critically, manipulate execution flow to execute arbitrary code with the privileges of the current user. This capability places the vulnerability within the MITRE ATT&CK framework under techniques associated with initial access and privilege escalation, specifically relating to exploitation for remote code execution through client-side applications like office productivity suites. The ability to execute code remotely makes this a high-severity threat that can lead to full system compromise if not mitigated promptly.
Mitigation strategies primarily involve applying the latest security patches released by Microsoft to update Excel and related Office components, ensuring that known flaws in memory management are addressed. Organizations should also enforce strict email filtering policies to block attachments from untrusted sources and disable automatic macro execution where possible. User awareness training is essential to reduce the success rate of social engineering attacks that deliver such malicious files. Additionally, deploying application whitelisting or data execution prevention mechanisms can help prevent the successful exploitation of memory corruption vulnerabilities by restricting unauthorized code execution in sensitive processes.