CVE-2026-108440 in Office 365 for Mac
Summary
by MITRE • 10/16/2026
Stack-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Word application, specifically manifesting as a stack-based buffer overflow condition that can be exploited remotely via a network connection. This type of vulnerability arises when a program writes more data to a fixed-length block of memory on the call stack than it is allocated to hold. In the context of Microsoft Office Word, this typically occurs during the processing of specific document formats or embedded objects where input validation mechanisms are insufficient. An attacker can craft a malicious file containing oversized data structures that, when opened by a victim using the vulnerable version of Word, cause the application to overwrite adjacent memory locations on the stack. This overwriting often targets critical control flow data such as return addresses or exception handler pointers, allowing the attacker to redirect the execution flow of the process to arbitrary code injected into the buffer itself or elsewhere in the process memory space.
From a technical perspective, this flaw aligns with Common Weakness Enumeration (CWE) identifiers such as CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write on Stack. The exploitation mechanism relies heavily on the lack of proper bounds checking during the parsing or rendering phases of document processing. When Word processes a specially crafted file, it fails to verify that the incoming data fits within the pre-allocated stack buffer limits. Consequently, excess bytes spill over into neighboring memory regions, corrupting the program's state. If an attacker can control these overwritten values, they gain the ability to execute arbitrary commands with the privileges of the user running the application. This is particularly dangerous because Microsoft Office applications are frequently used in enterprise environments where users open documents from various sources, including email attachments and network shares, increasing the attack surface significantly.
The operational impact of this vulnerability is severe, as it enables unauthorized remote code execution without requiring any additional interaction beyond opening or previewing a malicious document. This means that an attacker does not need to trick the user into clicking on links or running separate executables; simply viewing the content in Word can trigger the exploit. Once executed, the malicious code runs with the same security context as the current user, which often includes administrative privileges if the user is part of a privileged group. This allows for full system compromise, including the installation of malware, data theft, credential harvesting, and lateral movement within a network infrastructure. The ability to execute code over a network makes this vulnerability highly attractive to automated worm-like attacks that can propagate rapidly across connected systems without human intervention.
To mitigate the risks associated with this stack-based buffer overflow, organizations should prioritize immediate patching of all affected Microsoft Office versions using official security updates provided by Microsoft. These patches typically include enhanced input validation routines and memory protection mechanisms designed to detect and prevent such overflows before they can corrupt critical memory structures. Additionally, implementing application control policies that restrict the execution of untrusted scripts or macros within Office applications can reduce the impact if an exploit is attempted. Enabling Protected View for documents received from uncertain sources adds a layer of isolation by opening files in a sandboxed environment where potentially malicious code cannot interact with the host system's resources. Furthermore, deploying network-level security controls such as intrusion detection systems that monitor for anomalous traffic patterns associated with known exploitation attempts can provide an additional defense-in-depth measure against remote attacks targeting this vulnerability.