CVE-2026-108443 in Office
Summary
by MITRE • 10/16/2026
Off-by-one error 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 document parsing engine of Microsoft Office Word, specifically involving an off-by-one memory corruption issue. This type of defect typically arises when software performs boundary checks on data structures but fails to account for edge cases where input length matches or slightly exceeds expected limits by exactly one unit. In the context of Word processing documents, this often occurs during the parsing of complex formatting codes, embedded objects, or specific metadata fields within a .docx file. When an attacker crafts a malicious document containing specially constructed data that triggers this boundary miscalculation, it results in writing memory beyond the allocated buffer space. This out-of-bounds write can corrupt adjacent heap structures or overwrite critical control flow pointers such as return addresses on the stack.
From a technical perspective, this flaw aligns with CWE-193, which defines an off-by-one error leading to a buffer overflow. The exploitation of this vulnerability allows for arbitrary code execution because the attacker gains the ability to manipulate memory contents in a way that redirects program flow. By carefully crafting the payload within the malicious document, an adversary can overwrite function pointers or exception handler records with shellcode addresses. When Word attempts to process further operations on the corrupted data structure, it executes the injected instructions rather than its intended logic. This mechanism is particularly dangerous because it does not require user interaction beyond opening the file, provided that automatic content processing features are enabled for the document type in question.
The operational impact of this vulnerability is severe due to its potential for remote code execution over a network. An attacker can distribute the malicious Word document via email attachments, shared network drives, or web downloads. Upon receipt and subsequent opening by a victim, the exploit chain activates silently in the background without requiring macro enablement if it targets native parsing routines. This capability effectively compromises the integrity of the affected system, granting the attacker full control over the user environment with the privileges associated with the current process context. Consequently, this can lead to data exfiltration, installation of additional malware such as ransomware or backdoors, and lateral movement within an enterprise network if the compromised machine serves as a pivot point for further attacks against other internal resources.
In terms of threat modeling, this vulnerability is frequently associated with ATT&CK technique T1203, which covers Exploitation for Client Execution. Attackers leverage trusted applications like Microsoft Office to bypass security controls and establish persistence on target systems. The use of a document file as the delivery vector places it within the initial access phase of an attack lifecycle, specifically under techniques involving spearphishing attachments or drive-by downloads if hosted online. Because Word is ubiquitous in corporate environments, this vulnerability presents a high-risk surface area for targeted campaigns aimed at stealing sensitive intellectual property or disrupting business operations through system compromise.
Mitigation strategies must focus on both immediate remediation and long-term defense-in-depth measures. The primary corrective action involves applying the latest security updates released by Microsoft to patch the specific memory handling routines responsible for this off-by-one error. Organizations should ensure that all endpoints running affected versions of Office are updated promptly through automated deployment tools or manual intervention depending on their infrastructure scale. Additionally, administrators can mitigate risk by disabling automatic content processing features in Word settings, thereby preventing certain types of malicious payloads from executing upon document open without explicit user consent. Implementing application whitelisting policies and restricting the execution of scripts within temporary directories where downloaded documents are often stored can further reduce the attack surface. Endpoint detection and response solutions should also be configured to monitor for anomalous behavior patterns indicative of memory corruption exploits, such as unexpected process creation or heap spraying activities originating from Word processes.