Description

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

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-11T17:19:04.130Z",
  "pubdate": "2026-08-11T17:19:04.130Z",
  "executiveSummary": "A type confusion vulnerability, categorized as CWE-843 (Access of Resource Using Incompatible Type), exists within Microsoft Office Excel. This security flaw enables an unauthorized, local attacker to execute arbitrary code on the target system.\nThe vulnerability arises when Microsoft Office Excel improperly handles objects in memory, leading to a mismatch between the expected data type and the actual data type processed by the application.\nSuccessful exploitation allows an adversary with local access to manipulate memory structures, bypass security boundaries, and execute code within the security context of the currently logged-in user.\nThe primary impact of this vulnerability is local code execution, which can lead to complete system compromise, data exfiltration, or lateral movement depending on user privileges.\nWhile the attack requires local access to the system, exploitation typically involves tricking a user into opening a specially crafted malicious Excel file.\nRisk implications are significant for environments where users routinely handle untrusted spreadsheet documents, as successful exploitation requires no prior authentication to the vulnerable application component itself.",
  "technicalDetails": "The root cause of the vulnerability resides in memory management inconsistencies within Microsoft Office Excel when parsing complex or malformed spreadsheet structures. Specifically, the application fails to adequately verify the data types of objects allocated or referenced in memory.\nWhen a specially crafted Excel file is processed, the parser treats a resource as an incompatible type, resulting in incorrect object casting or memory offset calculations.\nThe vulnerable component involves the internal parsing engine responsible for interpreting specific file format records and managing internal object states within Microsoft Office Excel.\nThe attack flow begins when an unauthorized attacker delivers a malicious file to the target machine via local means or social engineering vectors.\nUpon opening the malicious file, Microsoft Office Excel instantiates the corrupted object structures in memory, triggering the type confusion condition during runtime execution.\nBecause the application assumes an incorrect data type, the attacker can achieve arbitrary read/write primitives within the process memory space.\nThese corrupted memory pointers are subsequently leveraged to redirect execution flow to attacker-supplied shellcode or Return-Oriented Programming (ROP) chains.\nExploitation requires local presence and user interaction to open the malicious document, but does not necessitate network exposure or prior authentication.\nPrivilege requirements are limited to the access rights of the user running the affected instance of Microsoft Office Excel.\nPost-exploitation impact includes arbitrary code execution, enabling the adversary to install backdoors, escalate privileges if auxiliary flaws exist, access sensitive data, or compromise the integrity of the host system."
}