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": "2026-08-11T17:19:03.400Z",
  "pubdate": "2026-08-11T17:19:03.400Z",
  "executiveSummary": "This vulnerability is classified as a heap-based buffer overflow affecting Microsoft Office Excel. The flaw allows an unauthorized attacker to achieve local code execution under the security context of the currently logged-in user. The vulnerability impacts systems utilizing vulnerable versions of Microsoft Office Excel, introducing significant risk to endpoint integrity and confidentiality.\nExploitation requires the targeted user to open a specially crafted malicious file using the vulnerable application. Upon successful processing of the malformed input, memory corruption occurs within the heap structure. An attacker with local access or the ability to deliver the payload via social engineering vectors can leverage this condition to execute arbitrary machine code, potentially leading to complete system compromise, unauthorized data access, or lateral movement within the enterprise environment.",
  "technicalDetails": "The vulnerability resides in the memory management logic of Microsoft Office Excel when parsing specific file formats and structures. Specifically, a heap-based buffer overflow occurs due to insufficient boundary checks and inadequate input validation prior to allocating and writing data into heap buffers.\nThe root cause stems from the application improperly calculating the required buffer size when processing malformed or malicious parsing instructions embedded within a workbook. When Excel processes these crafted records, an integer discrepancy or overflow allows input data to exceed the allocated boundaries of the heap chunk, resulting in a heap overflow condition.\nExploitation occurs step-by-step through the following attack flow: First, an attacker crafts a malicious file containing oversized or manipulated data structures designed to target specific heap layout allocations. Second, the victim opens the malicious file using Microsoft Office Excel. Third, as the application parses the corrupted file format, the vulnerable component allocates a heap buffer of insufficient size. Fourth, subsequent parsing routines copy data into the undersized buffer without verifying input length, thereby overflowing adjacent heap memory chunks.\nThis memory corruption overwrites adjacent heap metadata or critical function pointers. When the application later attempts to dereference or execute the corrupted pointers, execution flow is redirected to attacker-controlled shellcode or a return-oriented programming chain. The payload executes with the privileges of the local user running Microsoft Office Excel, enabling unauthorized code execution, installation of persistent backdoors, and further post-exploitation activities.\nThe attack vector requires local execution as the attacker must entice the victim to open the malicious file. Authentication requirements are none for the initial file delivery, and network exposure is not strictly required if the file is delivered via local storage, removable media, or alternative offline vectors."
}