CVE-2026-83891 in Office
Summary
by MITRE • 10/14/2026
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 • 10/14/2026
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 or entirely absent. An attacker can craft a malicious file containing specially designed content that triggers this overflow condition when opened by a victim using the vulnerable version of Word. The excessive data overwrites adjacent memory locations on the stack, potentially including critical control structures such as return addresses and saved frame pointers.
From a technical perspective, this flaw aligns with Common Weakness Enumeration identifier CWE-121, which defines stack-based buffer overflow. When the overwritten return address points to shellcode injected into the same buffer or another accessible memory region, the attacker gains arbitrary code execution capabilities on the target system. This exploitation vector is particularly dangerous because it allows for remote code execution without requiring user authentication in many scenarios, provided the victim opens the malicious document. The attack often leverages social engineering tactics where users are tricked into opening a seemingly legitimate file that contains embedded exploits targeting specific rendering engines or parsing libraries within Word.
The operational impact of this vulnerability is severe, as successful exploitation grants an unauthorized attacker full control over the affected system. This can lead to complete compromise of confidentiality, integrity, and availability of data stored on the machine. Attackers may install malware, create backdoors for persistent access, exfiltrate sensitive information, or use the compromised host as a pivot point to attack other systems within the internal network. Given that Microsoft Office is ubiquitous in enterprise environments, this vulnerability poses a significant risk to organizational security postures and can serve as an initial entry vector for broader cyberattacks including ransomware deployment or advanced persistent threat campaigns.
In terms of classification under industry frameworks, this vulnerability corresponds to MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution. It also relates to techniques involving file creation and execution such as T1564. The remote nature of the exploit means it falls under network-based attack vectors rather than local privilege escalation paths initially. Defense in depth strategies are essential here since client-side applications like Word have a large attack surface due to their complexity and ability to process diverse document types including those with macros, embedded objects, and rich text formatting features that may contain vulnerable code paths.
Mitigation efforts should prioritize immediate patching of all affected Microsoft Office versions through official security updates provided by the vendor. Organizations must ensure that automatic update mechanisms are enabled for office productivity suites to reduce exposure windows. Additionally implementing application control policies such as AppLocker or Windows Defender Application Control can prevent unauthorized executables from running even if an exploit succeeds in dropping payload files. User awareness training is also critical to mitigate social engineering aspects of this attack vector by teaching employees to recognize suspicious attachments and links. Network segmentation and endpoint detection and response solutions should be deployed to monitor for anomalous behavior indicative of exploitation attempts, such as unusual process creation patterns or network connections originating from office applications.