CVE-2026-78526 in Office
Summary
by MITRE • 09/09/2026
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 • 09/09/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Word application, specifically manifesting as a heap-based buffer overflow condition. This type of memory corruption error occurs when a program writes data beyond the allocated boundaries of a buffer located in the computer's random access memory, known as the heap. In the context of Microsoft Office Word, this defect is typically triggered by processing specially crafted documents or files that contain malformed content structures. When an attacker constructs a malicious file with precisely calculated payload sizes and offsets, they can overwrite adjacent memory locations on the heap. This overwriting capability allows for arbitrary code execution because the attacker can manipulate function pointers or exception handling mechanisms within the application's process space to redirect control flow toward their injected shellcode.
The operational impact of this vulnerability is severe due to its potential for remote code execution without user interaction beyond opening a malicious document, depending on the specific configuration and security settings in place. An unauthorized attacker who successfully exploits this flaw can execute arbitrary commands with the same privileges as the current user. If the affected user operates with administrative rights or elevated permissions, the attacker may gain full control over the compromised system. This enables subsequent actions such as installing malware, stealing sensitive data, creating new accounts for persistent access, or using the machine as a pivot point to attack other systems within the network infrastructure. The ability to execute code over a network significantly increases the risk surface, allowing attackers to target vulnerable machines remotely via email attachments, shared drives, or web-based document viewers that render Word content.
From a technical classification perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-120, which describes buffer copy without checking size limits, and more specifically points toward heap corruption dynamics often associated with CWE-787 out-of-bounds write vulnerabilities. In the context of cyber attack frameworks such as MITRE ATT&CK, exploitation of this flaw falls under techniques related to initial access through spearphishing attachments or drive-by compromise if hosted on a malicious website. The subsequent code execution phase maps directly to command and script interpreter abuse or process injection tactics, depending on how the attacker leverages the heap overflow to establish persistence or escalate privileges within the compromised environment.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided security patches that address the underlying memory management errors in the Word application binary files. Organizations should ensure that all Microsoft Office components are updated to the latest stable release containing these fixes. Additionally, implementing strict email filtering policies and disabling macro execution by default can reduce the likelihood of users inadvertently triggering malicious content. Network segmentation and endpoint detection and response solutions also play a crucial role in limiting lateral movement if an initial compromise occurs. Users should be educated on recognizing suspicious file sources and avoiding opening documents from untrusted origins to minimize exposure to such exploitation attempts.