CVE-2026-77911 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.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as an out-of-bounds read within Microsoft Office Word represents a critical memory safety flaw that compromises the confidentiality of system data through remote exploitation vectors. This specific type of error occurs when the application attempts to access memory locations beyond the intended boundaries of a buffer or array, typically due to insufficient validation of input parameters during the parsing and rendering of document content. In the context of Microsoft Office Word, this often manifests when processing complex documents containing specially crafted elements such as embedded objects, macros, images, or specific formatting structures that trigger malformed logic within the underlying rendering engine. When an attacker crafts a malicious file designed to exploit this condition, they can force the application to read from memory regions it should not access, potentially revealing sensitive information stored in adjacent memory blocks.
From a technical perspective, out-of-bounds reads are classified under CWE-125, which describes situations where software reads data past the end or before the beginning of the intended buffer. This flaw differs significantly from out-of-bounds writes because it generally does not allow for arbitrary code execution directly; instead, its primary impact is information disclosure. The attacker leverages this vulnerability to extract sensitive data such as cryptographic keys, session tokens, passwords, or other confidential information residing in the process memory space of the Word application. This capability transforms a simple document viewing action into a potent attack vector for espionage and credential theft, particularly when users are tricked into opening maliciously constructed files via email attachments or shared network drives.
The operational impact of this vulnerability is severe due to its potential for remote exploitation without user interaction beyond initial file opening. Attackers can distribute the exploit through phishing campaigns where victims receive seemingly legitimate documents that contain the payload triggering the memory read error. Once executed, the malicious code reads sensitive data from the application's memory and transmits it back to a command-and-control server over the network. This aligns with ATT&CK techniques related to Collection via Input Capture or Data from Local System, specifically focusing on stealing information through exploitation of client software rather than installing persistent malware agents. The ability to disclose information remotely makes this vulnerability particularly dangerous in enterprise environments where sensitive documents are frequently shared and opened by employees who may not have advanced technical security awareness.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Organizations should immediately apply the latest cumulative updates provided by Microsoft, which include patches for these memory safety issues to ensure that boundary checks are correctly enforced during document processing. Additionally, implementing application control policies can restrict the execution of untrusted scripts or macros within Office applications, thereby reducing the attack surface even if a vulnerability is present. Users must be educated on social engineering tactics and advised against opening documents from unknown sources. Furthermore, deploying advanced endpoint detection and response solutions that monitor for anomalous memory access patterns or unusual network connections originating from office productivity suites can help detect exploitation attempts in real time before significant data exfiltration occurs.