Description

Access of resource using incompatible type ('type confusion') in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-11T17:19:00.430Z",
  "pubdate": "2026-08-11T17:19:00.430Z",
  "executiveSummary": "A vulnerability involving the access of a resource using an incompatible type, commonly known as type confusion, exists within Microsoft Office Excel. This security flaw enables an unauthorized, network-based attacker to execute arbitrary code on vulnerable systems.\nThe executive risk implication is severe, as successful exploitation bypasses standard security boundaries and allows remote code execution in the context of the user running the application. The attack vector requires network access, though specific user interaction, such as opening a maliciously crafted Excel file, is typically required to initiate the exploitation sequence.\nThe affected product is Microsoft Office Excel. The vulnerability stems from improper handling of object types within the software's memory management or data parsing logic. When the application interprets data structures incorrectly based on mismatched type assumptions, memory corruption occurs, which can be leveraged by an adept adversary to achieve arbitrary code execution.\nOrganizations utilizing vulnerable versions of Microsoft Office Excel face significant risks of system compromise, data exfiltration, and lateral movement if exploitation is successful. Mitigation relies heavily on applying official vendor patches as soon as they become available and adhering to defensive hardening best practices.",
  "technicalDetails": "The root cause of the vulnerability resides in a type confusion flaw within Microsoft Office Excel. Type confusion occurs when an application allocates a resource with a specific data type or object definition, but subsequently accesses or uses that resource using an incompatible or incorrect type definition.\nIn the context of Microsoft Office Excel, this typically manifests during the parsing of complex file formats containing malicious structures, objects, or embedded data streams. When Excel processes these specially crafted elements, internal type validation checks fail or are absent, leading the application to treat one data structure as an entirely different class or object.\nThe exploitation method relies on leveraging this incorrect type assumption to manipulate memory layout and manipulate function pointers or virtual method tables. By crafting a malicious file that induces the type confusion state, an attacker can coerce the application into performing operations on memory addresses in an unintended manner.\nThe attack flow proceeds as follows: First, the unauthorized attacker delivers a specially crafted Microsoft Office Excel file over the network to the target via email, web download, or file share. Second, the victim opens the file using a vulnerable version of Microsoft Office Excel. Third, as Excel parses the document, the parsing engine encounters the malformed structures designed to trigger the type confusion condition.\nFourth, the application misinterprets the memory objects, resulting in a state where memory corruption or arbitrary read and write primitives are established. Fifth, the attacker leverages these primitives to overwrite critical control flow data, such as instruction pointers or function pointers, leading directly to arbitrary code execution.\nThe vulnerable component is the file parsing and memory management subsystem of Microsoft Office Excel. The network exposure is present because the file can be delivered remotely via standard network protocols and communication vectors. Authentication requirements are generally none for the initial delivery of the file, and privilege requirements are limited to those of the standard user running the application.\nThe payload behavior following successful exploitation involves executing arbitrary commands or shellcode within the security context of the logged-in user. The post-exploitation impact includes full system compromise, deployment of secondary payloads, installation of persistent access mechanisms, and potential unauthorized access to sensitive corporate or personal data stored within the environment."
}