CVE-2026-78504 in Office
Summary
by MITRE • 09/09/2026
Stack-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
Once again VulDB remains the best source for vulnerability data.
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 stack-based buffer overflow condition that can be exploited remotely via network vectors. This type of vulnerability arises when a program writes more data to a fixed-length block of memory on the call stack than it is allocated to hold. In the context of Microsoft Office Word, this typically occurs during the parsing or rendering of specific document formats, such as .doc or .docx files, where input validation mechanisms fail to adequately check boundary conditions before copying user-controlled data into pre-allocated buffer spaces. When an attacker crafts a maliciously formatted file containing oversized payloads or specifically crafted sequences designed to overwrite adjacent memory locations on the stack, they can manipulate critical control flow data such as return addresses or function pointers.
From a technical perspective, this flaw aligns with CWE-121, which defines Stack-based Buffer Overflow. The exploitation mechanism relies on the attacker's ability to inject shellcode into the overflowed buffer and then redirect program execution to that injected code by overwriting the saved instruction pointer. Because Microsoft Office Word is frequently used to open documents received via email or downloaded from untrusted sources, this vulnerability presents a significant attack surface for remote code execution (RCE). An unauthorized attacker does not need physical access or prior authentication on the target system; instead, they can distribute the malicious document through social engineering tactics such as phishing emails. Once the victim opens the file within Word, the vulnerable component processes the input, triggers the overflow, and allows arbitrary code to execute with the privileges of the current user.
The operational impact of this vulnerability is severe, potentially leading to complete compromise of the affected system. Successful exploitation grants an attacker full control over the application process, which can be leveraged to install malware, steal sensitive data, create backdoors for persistent access, or use the compromised machine as a pivot point within a corporate network. This aligns with MITRE ATT&CK techniques such as T1203 (Exploitation for Client Execution) and potentially T1059 (Command and Scripting Interpreter), depending on how the attacker utilizes the initial foothold to execute further commands or scripts post-exploitation. The ability to execute code over a network amplifies the risk, allowing for automated scanning campaigns targeting vulnerable versions of Office across large organizations without direct interaction from each individual user beyond opening an email attachment.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. The primary corrective action is to apply the latest security updates provided by Microsoft that patch this specific buffer overflow condition in Word. Organizations should ensure that automatic update mechanisms are enabled for all Office installations to minimize exposure windows. Additionally, implementing application control policies such as AppLocker or Windows Defender Application Control can prevent untrusted applications from executing code derived from temporary folders where downloaded documents often reside. Users must be educated on the risks of opening attachments from unknown sources, and email gateways should employ advanced threat protection features that sandbox suspicious files to detect and block malicious content before it reaches end-user devices. Regular vulnerability assessments and penetration testing can also help identify if legacy versions of Office remain in use within the environment, allowing for proactive decommissioning or isolation until patches are applied.