Description

Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-11T17:19:05.820Z",
  "pubdate": "2026-08-11T17:19:05.820Z",
  "executiveSummary": "A heap-based buffer overflow vulnerability has been identified within Microsoft Office Excel. This critical security flaw allows an unauthorized, local attacker to achieve arbitrary code execution on vulnerable systems. The vulnerability resides in the way Microsoft Office Excel processes maliciously crafted spreadsheet files, leading to memory corruption within the heap.\nSuccessful exploitation of this memory corruption vulnerability enables threat actors to execute arbitrary code with the privileges of the currently logged-in user. If the user possesses administrative or elevated privileges, the impact on the underlying operating system is severe, potentially leading to a complete compromise of system integrity, confidentiality, and availability.\nThe risk implications are high, as Microsoft Office Excel is a widely deployed enterprise application. The attacker capabilities involve local execution vectors, typically requiring social engineering to trick a target user into opening a specially crafted document. There are no specific complex network exposure requirements mentioned, as the primary vector relies on local file handling, though delivery can be facilitated via phishing or network shares. Mitigation requires vigilance in opening untrusted documents and applying official vendor updates when available.",
  "technicalDetails": "The vulnerability is a classic heap-based buffer overflow stemming from improper bounds checking during the parsing of specific structural records within Microsoft Office Excel files. The vulnerable component is the file parser responsible for handling proprietary or open spreadsheet formats within the application binaries. When Microsoft Office Excel processes a malformed or maliciously manipulated file, it allocates a dynamic memory buffer on the heap that is insufficiently sized to accommodate the incoming parsed data.\nThe root cause lies in inadequate input validation and integer handling within the memory allocation routines. Specifically, when the application calculates the required buffer size based on metadata values embedded in the file, an integer mismatch or overflow can occur. This results in the allocation of a smaller heap chunk than required to store the subsequent payload data copied into it. As the parsing engine continues to write data beyond the boundaries of the allocated heap chunk, adjacent heap metadata or critical application structures are overwritten.\nThe exploitation method leverages this out-of-bounds write primitive to corrupt heap metadata, such as chunk headers, or overwrite adjacent function pointers and objects residing on the heap. By carefully structuring the layout of the heap through heap grooming or feng shui techniques—often achieved by embedding specific objects or manipulating memory allocations prior to triggering the overflow—an attacker can redirect control flow to shellcode or implement return-oriented programming (ROP) chains.\nThe attack flow proceeds in a sequential manner: first, the unauthorized attacker crafts a malicious Microsoft Office Excel file designed to exploit the buffer size calculation flaw. Second, the file is delivered to the target system via local transfer, email attachment, or network storage. Third, the victim opens the malicious file using a vulnerable version of Microsoft Office Excel. Fourth, the application attempts to parse the malformed structures, triggering the heap-based buffer overflow. Fifth, the resulting memory corruption alters application execution flow, culminating in the local execution of arbitrary attacker-supplied code.\nRegarding constraints and requirements, the vulnerability requires local access in the sense that the file must be processed by the local instance of the application. Authentication requirements are non-existent or trivial, as the attacker does not need to authenticate to the application to supply the malicious file. Privilege requirements are limited to standard user privileges; the malicious code executes within the security context of the user running Microsoft Office Excel. Network exposure is indirect, relying on the delivery vector of the file rather than a listening network service. The post-exploitation impact includes persistent local access, potential lateral movement within the network, and full compromise of user-accessible data."
}