CVE-2026-70254 in Office Excel
Summary
by MITRE • 10/14/2026
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 • 10/14/2026
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 is classified under Common Weakness Enumeration as CWE-125, which denotes Out-of-Bounds Read. The core technical issue arises when the software fails to properly validate array indices or buffer boundaries before accessing data in memory. In the context of Excel, this typically occurs during the parsing and rendering of complex spreadsheet files that contain specially crafted formulas, embedded objects, or malformed binary structures. When an attacker constructs a malicious document designed to exploit these boundary checks, they can trigger the application to read from memory locations outside the intended buffer limits. This improper validation allows for the leakage of sensitive information stored in adjacent memory regions, such as stack cookies, function return addresses, or other process data that should remain inaccessible to user-level applications.
The operational impact of this vulnerability is severe due to its potential for remote code execution over a network. Although an out-of-bounds read primarily facilitates information disclosure by default, sophisticated attackers can leverage the leaked memory contents to bypass security mitigations such as Data Execution Prevention and Address Space Layout Randomization. By carefully crafting the input data, an attacker may achieve arbitrary code execution with the privileges of the current user. This means that if a victim opens a malicious Excel file received via email or downloaded from a website, the attacker can execute commands on the compromised system without any interaction beyond opening the document. The attack vector is classified as network-based and remote, allowing exploitation across various platforms where Microsoft Office is installed, provided the vulnerability has not been patched by the vendor.
From an offensive security perspective, this flaw aligns with several tactics in the MITRE ATT&CK framework. It relates to Initial Access through spearphishing attachment techniques, where malicious documents are used as the delivery mechanism for exploitation. Once executed, it falls under Execution and potentially Privilege Escalation if the leaked memory data aids in bypassing system protections. The vulnerability highlights the risks associated with processing untrusted input from external sources without rigorous sanitization or boundary checks. Organizations must recognize that even read-only vulnerabilities can serve as stepping stones to full compromise when combined with other exploitation techniques like heap spraying or information leakage attacks.
To mitigate this risk, immediate action is required at both the organizational and individual levels. The primary defense is to apply the latest security updates released by Microsoft for all versions of Office Excel affected by this vulnerability. Administrators should prioritize patching systems that are exposed to network traffic or handle external documents frequently. In environments where patching cannot be immediately implemented, application control policies such as Windows Defender Application Control can restrict the execution of untrusted applications and scripts. Additionally, users should be educated on social engineering tactics, avoiding opening attachments from unknown senders and verifying the source of any unexpected files. Enabling Protected View for documents originating from the internet adds an extra layer of isolation by running Excel in a sandboxed environment with limited permissions, thereby preventing exploitation even if the vulnerability is present. Regular security awareness training and strict email filtering rules further reduce the likelihood of successful delivery of such malicious payloads.