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": "2026-08-11T17:19:03.140Z",
  "pubdate": "2026-08-11T17:19:03.140Z",
  "executiveSummary": "A heap-based buffer overflow vulnerability exists within Microsoft Office Excel, potentially allowing unauthorized attackers to achieve local code execution. This security flaw resides in the application's memory management handling of specific file structures or data parsing operations.\nThe primary impact of successful exploitation is arbitrary code execution with the privileges of the currently logged-in user. If the user possesses administrative privileges, the compromise could extend to complete system takeover. The affected system is Microsoft Office Excel, impacting local processing environments where malicious documents are opened.\nThe risk implications are severe due to the potential for stealthy execution and persistence upon successful exploitation. Attacker capabilities are constrained by the requirement for local interaction, typically necessitating that a victim open a specially crafted malicious file using the vulnerable software.\nExploitation requirements center around social engineering or local file delivery to induce the target user into opening the malformed spreadsheet. No explicit authentication is required by the attacker to construct the malicious payload, but local execution context is mandatory.",
  "technicalDetails": "The vulnerability is a classic heap-based buffer overflow stemming from improper bounds checking during the parsing of complex or malformed file formats within Microsoft Office Excel. The vulnerable component involves internal memory allocation routines responsible for handling specific record types or data structures within spreadsheet files.\nRoot cause analysis indicates that when Microsoft Office Excel processes a specially crafted file, it fails to adequately validate the size of incoming data prior to writing it into a dynamically allocated heap buffer. This size discrepancy allows an attacker to supply input that exceeds the allocated buffer dimensions, leading to out-of-bounds memory writes on the heap.\nThe attack flow initiates when an unauthorized attacker crafts a malicious spreadsheet containing corrupted or oversized structural metadata. The victim downloads or receives this file and opens it locally using Microsoft Office Excel. As the parsing engine iterates through the malicious records, the heap buffer overflow is triggered due to the lack of strict input sanitization and boundary verification.\nDuring exploitation, the overflow overwrites adjacent heap metadata or critical function pointers residing within the heap memory space. By meticulously arranging the heap layout through heap feng shui techniques, an attacker can manipulate adjacent objects to redirect execution flow upon subsequent function calls or object destructions.\nAuthentication requirements are nonexistent for the initial payload construction, as the attack is delivered via a static file. Privilege requirements are limited to standard user privileges, meaning the malicious code executes within the security context of the user running Microsoft Office Excel. Network exposure is indirect, relying on the delivery mechanism of the file via email, web download, or local network shares rather than a direct network listener.\nPayload behavior following successful redirection typically involves the execution of shellcode designed to drop secondary payloads, establish command and control channels, or perform local reconnaissance. Post-exploitation impact encompasses total compromise of the user session, data exfiltration, lateral movement within the network, and potential escalation of privileges if auxiliary vulnerabilities or misconfigurations are present."
}