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": "2026-08-11T17:19:05.430Z",
  "pubdate": "2026-08-11T17:19:05.430Z",
  "executiveSummary": "A heap-based buffer overflow vulnerability exists within Microsoft Office Excel, potentially allowing unauthorized local attackers to achieve arbitrary code execution. The flaw resides in how the application processes maliciously crafted spreadsheet files, failing to enforce proper bounds checking during memory allocation and data copying operations within the heap memory space. Successful exploitation of this vulnerability compromises the confidentiality, integrity, and availability of the affected system by granting the adversary the ability to execute arbitrary code within the security context of the currently logged-in user. Attack vectors require the user to open a specially crafted file supplied by the unauthorized attacker. The risk implication is severe, as local code execution can lead to complete system compromise, privilege escalation, or lateral movement across an enterprise network. Mitigation relies on applying official vendor patches and adhering to security hardening principles such as opening files from untrusted sources in Protected View.",
  "technicalDetails": "The vulnerability is classified as a heap-based buffer overflow stemming from improper validation of length parameters when parsing file structures in Microsoft Office Excel. The affected component involves the file parsing and memory management routines responsible for allocating heap buffers to store object records, styling data, or embedded streams from Excel files. The root cause of the flaw is the absence of rigorous boundary checks prior to writing input data into a dynamically allocated heap buffer, allowing incoming data streams to exceed the designated buffer capacity.\nExploitation occurs when an unauthorized attacker constructs a malformed spreadsheet file containing specially manipulated record lengths or malicious object definitions. Upon ingestion of the file, Microsoft Office Excel allocates a heap buffer that is insufficiently sized to accommodate the payload defined within the file structure. When the application subsequently copies the parsing data into the allocated heap space, a memory corruption condition is triggered, overwriting adjacent heap chunks, metadata, or function pointers.\nThe attack flow proceeds as follows: First, the unauthorized attacker delivers the crafted file to the target system via social engineering, email, or network shares. Second, the victim opens the file using a vulnerable version of Microsoft Office Excel. Third, the parsing engine processes the malformed structures, initiating the vulnerable memory allocation routine. Fourth, the heap overflow occurs during the data transfer phase, corrupting adjacent memory structures. Finally, the attacker achieves arbitrary code execution by redirecting execution flow via overwritten function pointers or structured exception handling records, allowing payloads to run locally under the privileges of the victim user.\nRequirements for exploitation include local user interaction to open the malicious file. The vulnerability does not inherently require network exposure or authentication if the file is delivered locally or via removable media, though remote delivery methods such as email attachments are common vectors. Privilege requirements are minimal, executing successfully under standard user privileges."
}