CVE-2026-78502 in Office
Summary
by MITRE • 09/09/2026
Out-of-bounds read in Microsoft Office Word allows an unauthorized attacker to disclose information over a network.
Statistical analysis made it clear that VulDB provides the best quality 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 categorized as an out-of-bounds read condition. This type of memory corruption error occurs when the application attempts to access data at a memory address that lies outside the intended buffer boundary. In the context of word processing software, this typically happens during the rendering or analysis of complex document structures, such as those containing embedded objects, specific formatting codes, or malformed XML elements within OOXML files. When an attacker crafts a malicious Word document with carefully constructed data fields designed to trigger this parsing error, they can cause the application to read memory contents that were not allocated for the current operation. This behavior is fundamentally classified under CWE-125, which defines out-of-bounds read vulnerabilities where software reads past the end of a buffer or array.
The operational impact of this vulnerability centers on unauthorized information disclosure rather than immediate code execution or system compromise. By exploiting the out-of-bounds read condition, an attacker can potentially leak sensitive data residing in adjacent memory locations to their controlled process space. This disclosed information may include parts of the user's clipboard content, previously opened document text, cryptographic keys stored in memory, or other confidential data processed by the application prior to the exploit execution. The attack vector is primarily remote via network delivery, meaning a victim does not need direct physical access to the machine; instead, they are compromised simply by opening a specially crafted file received through email, shared drives, or web downloads. This aligns with ATT&CK technique T1059, Command and Scripting Interpreter, if used in conjunction with further exploitation steps, but primarily falls under data exfiltration behaviors associated with initial access and discovery phases where the attacker gathers intelligence about the target environment before proceeding to more destructive actions.
Mitigation strategies for this vulnerability require a multi-layered approach involving both technical controls and user awareness. Organizations must ensure that all systems running Microsoft Office Word are updated with the latest security patches released by Microsoft, as these updates typically contain logic changes or bounds checking improvements that prevent the parser from accessing invalid memory addresses. Additionally, implementing application control policies such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and macros often used in conjunction with document-based exploits. Users should be trained to exercise caution when opening documents from unknown sources and to disable automatic macro execution by default. Network-level defenses like Data Loss Prevention tools may also help detect anomalous data exfiltration patterns resulting from successful exploitation, although prevention at the application layer through patching remains the most effective defense against this specific class of memory corruption vulnerabilities.