CVE-2026-78505 in Office
Summary
by MITRE • 09/09/2026
Heap-based buffer overflow in Microsoft Office 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 suite, specifically manifesting as a heap-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 dynamically allocated memory block on the heap than it was intended to hold, leading to adjacent memory corruption. In the context of Microsoft Office applications, this flaw is typically triggered by processing specially crafted documents or files containing malformed content that exceeds expected buffer boundaries during parsing operations. The exploitation mechanism relies on manipulating these internal structures to overwrite critical data such as function pointers or exception handlers located in nearby heap regions, thereby gaining control over program execution flow.
From a technical perspective, the root cause aligns with CWE-122, which categorizes heap-based buffer overflows where memory is allocated dynamically using functions like malloc or new. The attacker crafts input that causes an integer overflow or miscalculation in size determination, allowing for excessive data injection into a fixed-size buffer on the heap. This corruption disrupts the internal state of the Office application process, potentially leading to arbitrary code execution with the privileges of the currently logged-in user. Since Microsoft Office is widely deployed across enterprise environments and frequently handles untrusted documents received via email or shared drives, this vulnerability presents a significant attack surface for remote exploitation without requiring physical access or local authentication beyond initial document opening.
The operational impact of successfully exploiting this heap-based buffer overflow is severe, as it enables an unauthorized attacker to execute arbitrary code on the target system over a network connection. This capability allows adversaries to install malware, steal sensitive data, create new accounts with administrative privileges, or pivot further into internal networks. The attack vector corresponds closely to MITRE ATT&CK techniques involving remote code execution through application vulnerabilities, often leveraging social engineering tactics such as phishing emails containing malicious Office documents to trigger the exploit upon opening. Because modern operating systems employ various memory protection mechanisms like Data Execution Prevention and Address Space Layout Randomization, successful exploitation may require additional steps such as information disclosure or specific payload construction to bypass these defenses, yet the potential for full system compromise remains high if mitigations are not in place.
To mitigate this risk, organizations must ensure that all Microsoft Office installations are updated with the latest security patches released by Microsoft addressing this specific vulnerability. Administrators should also consider implementing application control policies using tools like Windows Defender Application Control or AppLocker to restrict which applications can execute code from certain directories, thereby limiting the impact of any successful exploitation. Additionally, enabling Protected View for documents received from untrusted sources adds a layer of isolation that prevents potentially malicious content from executing in the main process context. Network-level defenses such as intrusion detection systems should be configured to detect and block traffic patterns associated with known exploit attempts targeting Office applications, while user awareness training remains essential to prevent social engineering attacks that deliver the initial malformed documents triggering this heap overflow condition.