CVE-2026-108439 in Office
Summary
by MITRE • 10/16/2026
Heap-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 • 10/17/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Word application, specifically manifesting as a heap-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 dynamically allocated block of memory on the heap than it was intended to hold, leading to adjacent memory corruption. In the context of Microsoft Office Word, this flaw is typically triggered by processing specially crafted documents or files containing malformed content that exceeds expected buffer boundaries during parsing operations. The exploitation vector being network-based indicates that an attacker does not need physical access or local user privileges on the target machine; instead, they can deliver a malicious payload through email attachments, shared drives, or web-hosted documents accessed via browser plugins or integrated viewing mechanisms.
From a technical perspective, heap overflows are particularly dangerous because the heap is used for dynamic memory allocation during program execution, and corrupting this area allows attackers to overwrite critical data structures such as function pointers, exception handlers, or object vtables. By carefully crafting the overflow payload, an attacker can gain control over the instruction pointer of the vulnerable process. This enables arbitrary code execution with the privileges of the user running Microsoft Office Word. If the victim is logged in with administrative rights, the compromise could escalate to full system takeover, allowing the installation of malware, data exfiltration, or lateral movement within a corporate network. The severity is further amplified by the ubiquity of Microsoft Office products and the common practice of opening documents from external sources without rigorous verification.
This vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-120: Buffer Copy without Checking Size of Input, which describes the fundamental error of copying data into a buffer without verifying its length against the allocated size. Additionally, it relates to CWE-787: Out-of-bounds Write on Heap, highlighting the specific memory region affected. In terms of offensive security frameworks like MITRE ATT&CK, this exploit scenario maps to techniques involving Initial Access through Spearphishing Attachment or Drive-by Compromise, followed by Execution via User Interaction and potentially Privilege Escalation if elevation exploits are chained with the initial heap overflow. The ability to execute code over a network places it in high-risk categories for automated scanning campaigns and targeted phishing attacks aimed at enterprise environments.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. Organizations should immediately apply vendor-provided security patches or updates that address this specific buffer overflow issue, ensuring that all instances of Microsoft Office Word are updated to the latest secure version. Network segmentation can help limit exposure by restricting access to document sharing services from untrusted networks. Furthermore, implementing application whitelisting and disabling macro execution for documents received from external sources reduces the attack surface significantly. Security awareness training is also critical, as user vigilance in identifying suspicious attachments remains a primary defense against social engineering tactics that deliver such exploits. Regular vulnerability assessments and penetration testing should be conducted to identify similar memory corruption flaws before they can be exploited by malicious actors.