CVE-2026-78507 in 365 Apps for Enterprise
Summary
by MITRE • 09/09/2026
Use after free in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described constitutes a critical security flaw within the document parsing engine of Microsoft Office Word, specifically involving improper memory management during the handling of complex file structures. This issue is classified as a use-after-free error, which occurs when software continues to reference a block of memory after it has been freed or deallocated by the system. In the context of Microsoft Office applications, this typically happens when an attacker crafts a malicious Word document containing specially formatted elements that trigger specific parsing routines. When the application processes these malformed structures, it may release certain data buffers while retaining pointers to them in internal object references. Subsequent operations on those dangling pointers allow for arbitrary memory writes or reads, effectively bypassing standard security boundaries and enabling remote code execution with the privileges of the current user.
From a technical perspective, this flaw aligns closely with Common Weakness Enumeration identifier CWE-416, which defines use-after-free vulnerabilities as conditions where an application uses memory after it has been freed. The operational impact is severe because Microsoft Office applications are frequently used to open documents received from external sources via email or network shares. An attacker can host a malicious document on a web server and trick the victim into opening it through social engineering, such as embedding a link in an email that appears legitimate. Upon execution of the parsing logic triggered by the crafted file, the vulnerability allows for arbitrary code execution within the context of the logged-on user. This means that if a user opens the malicious document with administrative privileges, the attacker gains full control over the system, potentially installing malware, stealing sensitive data, or pivoting to other systems on the network.
This attack vector is consistent with techniques observed in advanced persistent threat campaigns and aligns with MITRE ATT&CK tactics related to initial access and execution. Specifically, it relates to T1566.002, which covers Spearphishing Attachment attacks where malicious files are used as a delivery mechanism for exploits. The ability to execute code over the network highlights the risk associated with default configurations that allow automatic processing of embedded objects or macros without sufficient user interaction warnings in certain legacy versions. While modern iterations of Office have implemented enhanced protection features like Protected View, older versions or specific configuration settings may still be susceptible if users disable these safeguards or are targeted by sophisticated phishing campaigns designed to bypass such controls.
Mitigation strategies must focus on both technical controls and administrative policies. The primary defense is the immediate application of security patches provided by Microsoft that address this memory corruption issue in affected versions of Office Word. Organizations should ensure their patch management processes are rigorous and timely, prioritizing updates for office productivity suites due to their high exposure surface area. Additionally, implementing strict email filtering rules can help block attachments from unknown senders or those containing executable content disguised as documents. User awareness training is equally critical; employees must be educated on the risks of opening unsolicited files and recognizing social engineering tactics designed to induce them into disabling security features like Protected View. Network segmentation should also be considered to limit the potential blast radius if a workstation becomes compromised, ensuring that lateral movement from an initial exploit is restricted by firewall rules and access control lists.