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": "2026-08-11T17:19:05.303Z",
  "pubdate": "2026-08-11T17:19:05.303Z",
  "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 achieve arbitrary code execution on vulnerable systems.\nThe vulnerability manifests when Microsoft Office Excel improperly handles object types during the parsing and processing of maliciously crafted spreadsheet files. Because the application fails to adequately verify the data types of resources before performing operations on them, an attacker can manipulate memory structures in a way that leads to unexpected behaviors, such as out-of-bounds memory access or arbitrary write primitives.\nSuccessful exploitation requires the attacker to trick a user into opening a specially crafted Excel file locally, or otherwise deliver the payload through an execution vector where the user interacts with the malicious document. Once the file is processed by the vulnerable Microsoft Office Excel component, the attacker can leverage the type confusion condition to execute code within the security context of the currently logged-on user.\nThe risk implications are severe, as arbitrary code execution can lead to complete system compromise, data exfiltration, or lateral movement within the network if the affected user possesses elevated privileges. Mitigating this risk requires applying official vendor patches and implementing defense-in-depth measures such as Office security hardening and file restriction policies.",
  "technicalDetails": "The root cause of this vulnerability stems from a type confusion flaw (CWE-843) residing within the memory management and object handling routines of Microsoft Office Excel. Specifically, the vulnerable component misinterprets the type of an object allocated in memory, treating it as a different data type than intended.\nWhen Microsoft Office Excel parses complex spreadsheet files containing embedded objects, charts, or specialized formatting structures, it allocates specific memory buffers and assigns internal type descriptors. Due to insufficient type checking and validation logic, a maliciously crafted file can induce the application to instantiate an object of one type and subsequently interact with it using methods or properties associated with an incompatible type.\nThe step-by-step attack flow typically commences when an unauthorized attacker constructs a malformed spreadsheet file designed to manipulate internal memory layouts. The attacker delivers this file to the target victim via local file transfer, removable media, or social engineering vectors. Upon opening the file, Microsoft Office Excel invokes its internal parsers to process the malicious structures.\nDuring parsing, the type confusion condition is triggered when the application references the misidentified object. This discrepancy allows the attacker to corrupt adjacent memory regions, achieve arbitrary read/write capabilities, and bypass standard memory protections such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP).\nBy weaponizing the resulting memory corruption, the attacker redirects execution flow to malicious shellcode or executes return-oriented programming (ROP) chains. Because the exploitation occurs within the context of the running application, the resulting payload executes with the privileges of the local user. Network exposure is localized unless combined with a secondary remote execution vector, but the post-exploitation impact includes full application compromise and potential persistence on the host system."
}