CVE-2026-102855 in 365 Apps for Enterprise
Summary
by MITRE • 10/15/2026
Heap-based buffer overflow in Microsoft Office Visio allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Visio application, specifically manifesting as a heap-based buffer overflow. This type of memory corruption error occurs when a program writes more data to a dynamically allocated block of memory on the heap than it was intended to hold. In the context of Visio, this typically involves the processing of complex diagram files or specific vector graphics elements where input validation is insufficient. When an attacker crafts a malicious file containing oversized or malformed data structures, they can overwrite adjacent memory locations that contain control information such as return addresses or function pointers. This overwriting allows for arbitrary code execution with the privileges of the currently logged-in user, effectively granting full control over the affected system without requiring authentication.
From a technical perspective, this vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write. The root cause lies in the failure of the application to properly validate the size of incoming data before copying it into a fixed-size buffer on the heap. This lack of bounds checking is particularly dangerous because modern operating systems employ various memory protection mechanisms like Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR). However, sophisticated attackers can often bypass these protections using techniques such as Return-Oriented Programming or by exploiting specific allocator behaviors to achieve reliable code execution. The presence of this flaw indicates a significant gap in the secure coding practices applied during the development of Visio's file parsing engine.
The operational impact of this vulnerability is severe due to its network-vector nature, which classifies it under ATT&CK technique T1566 Phishing or potentially T1190 Exploit Public-Facing Application if delivered via web services. An attacker does not need physical access or local account privileges on the target machine; instead, they can distribute a malicious Visio file through email attachments, shared network drives, or compromised websites. Upon opening the crafted document, the exploit triggers automatically in many configurations, leading to immediate compromise of the workstation. This facilitates lateral movement within an enterprise environment, data exfiltration, and installation of persistent backdoors such as remote access trojans. Given that Visio is widely used in engineering, architecture, and IT sectors for creating technical diagrams, the potential attack surface is broad, affecting organizations with high-value intellectual property protected by these visual documents.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. The primary defense is to apply the latest security patches released by Microsoft that address this specific heap overflow issue in Visio. Organizations should enforce strict patch management policies to ensure all endpoints are updated promptly. Additionally, implementing application control solutions like Windows Defender Application Control or AppLocker can prevent unauthorized executables from running even if an exploit succeeds. Users must be educated on social engineering tactics and advised not to open unsolicited files, particularly those with double extensions or macros enabled by default. Network segmentation should also be utilized to limit the blast radius of a potential compromise, ensuring that infected machines cannot easily communicate with command-and-control servers or access sensitive internal resources. Regular vulnerability scanning and penetration testing can help identify similar weaknesses in other applications before they are exploited in the wild.