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": "2026-08-11T17:19:02.877Z",
  "pubdate": "2026-08-11T17:19:02.877Z",
  "executiveSummary": "This vulnerability is classified as a heap-based buffer overflow affecting Microsoft Office Excel. The flaw allows an unauthorized local attacker to achieve arbitrary code execution on the target system. The primary impact of successful exploitation includes complete compromise of the affected application process, leading to potential data exfiltration, system modification, or further lateral movement within the environment, all operating under the security context of the currently logged-in user.\nThe risk implications are severe due to the ubiquity of spreadsheet processing in enterprise environments, where users frequently open untrusted documents received via email or downloaded from external sources. Attack capabilities are constrained by the requirement for local interaction, specifically necessitating that the victim opens a maliciously crafted file using a vulnerable version of Microsoft Office Excel. Exploitation relies on memory corruption primitives to overwrite adjacent heap structures, redirecting execution flow to attacker-supplied shellcode.",
  "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 bounds checking and improper validation of size parameters during the allocation and copying of dynamic memory buffers within the vulnerable component.\nWhen a user opens a maliciously crafted Excel file, the application parses embedded record structures containing manipulated length or count fields. The parsing engine allocates an insufficient heap buffer based on these fraudulent values. Subsequent copy operations write data past the boundaries of the allocated heap chunk, corrupting adjacent heap metadata, function pointers, or critical application objects.\nThe exploitation method leverages this heap corruption to hijack the instruction pointer. By carefully arranging the heap layout via sophisticated file structures (often referred to as heap feng shui or heap grooming), the attacker ensures that predictable objects or function pointers are overwritten with malicious payload addresses. When the application subsequently invokes the corrupted pointer or object method, execution is redirected to shellcode embedded within the heap.\nAttack requirements mandate that the target system runs a vulnerable instance of Microsoft Office Excel. The attack flow proceeds as follows: first, the unauthorized attacker crafts a malicious document designed to exploit the heap corruption vulnerability; second, the file is delivered to the victim via local storage, removable media, or network shares; third, the victim opens the file within Excel, triggering the parser; fourth, the out-of-bounds write occurs during memory processing; and fifth, the execution flow is successfully hijacked, resulting in local code execution.\nBecause the execution occurs within the context of the Excel process, the privileges required are limited to those of the local user running the application. No prior authentication is required, but local user interaction in the form of opening the malicious file is necessary for successful exploitation."
}