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": "2026-08-11T17:19:04.503Z",
  "pubdate": "2026-08-11T17:19:04.503Z",
  "executiveSummary": "A heap-based buffer overflow vulnerability exists within Microsoft Office Excel, potentially enabling an unauthorized local attacker to achieve arbitrary code execution. The vulnerability resides in the application's memory management handling of specific file structures or parsing mechanisms. If successfully exploited, the flaw compromises the confidentiality, integrity, and availability of the affected system by allowing malicious code to execute within the security context of the currently logged-in user. The risk implication is high, as successful exploitation could lead to full system compromise or lateral movement within an organization if delivered via socially engineered file attachments. Attacker capabilities require the local execution or opening of a maliciously crafted Excel file by a targeted user, as remote network exposure is not inherently defined by the vector. Exploitation requirements mandate that the victim interacts with the malicious payload, typically through the file system or via local execution paths, triggering the flawed parsing logic in Microsoft Office Excel.",
  "technicalDetails": "The vulnerability is a classic heap-based buffer overflow stemming from improper bounds checking during the parsing of malformed data structures within Microsoft Office Excel. The affected component is responsible for allocating memory buffers on the heap to store parsed file contents or object attributes. When a crafted file containing oversized or specially manipulated records is processed, the application fails to validate the size of the input data against the allocated heap chunk boundaries. Consequently, writing operations exceed the allocated buffer size, resulting in contiguous heap memory corruption.\nThe root cause lies in insecure memory handling routines where dynamic buffer allocation sizes are calculated incorrectly or input lengths are blindly trusted without adequate sanitization. The exploitation method involves crafting a malicious document containing specifically engineered payload structures designed to manipulate the heap layout. When Microsoft Office Excel processes this input, the overflow overwrites adjacent heap metadata or critical application data structures, such as function pointers or virtual method tables.\nThe attack flow proceeds as follows: First, an unauthorized local attacker places or delivers a malicious file to the target system. Second, the user opens the file using Microsoft Office Excel. Third, the parsing engine encounters the malformed records and allocates an insufficient heap buffer. Fourth, the subsequent write operation overflows the heap boundary, corrupting adjacent memory. Fifth, the attacker redirects execution flow by overwriting targeted pointers with malicious shellcode addresses. Finally, the injected payload executes locally with the privileges of the victim user.\nAuthentication requirements are none locally, as the attack vector relies on file parsing rather than authenticated service interaction. Privilege requirements are limited to standard user privileges, meaning the attacker only needs the ability to execute the application and open the file. Network exposure is local, dependent on the delivery mechanism of the file rather than a listening network socket. Post-exploitation impact includes arbitrary code execution, installation of persistent backdoors, data exfiltration, and potential escalation of privileges depending on the local system configuration and applied hardening controls."
}