Description

Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-11T17:19:02.747Z",
  "pubdate": "2026-08-11T17:19:02.747Z",
  "executiveSummary": "A critical out-of-bounds read vulnerability has been identified in Microsoft Office Excel. This memory safety flaw allows an unauthorized local attacker to execute arbitrary code within the context of the current user. The vulnerability manifests when Microsoft Office Excel improperly parses maliciously crafted spreadsheet files, failing to validate boundary constraints during memory read operations.\nThe primary impact of successful exploitation is local code execution, which can lead to complete compromise of the user session, data exfiltration, and lateral movement depending on the privileges of the affected user. The attack vector requires the target user to open a specially crafted file supplied by the adversary, necessitating localized interaction or social engineering.\nAffected systems include vulnerable installations of Microsoft Office Excel. The risk implications are severe due to the ubiquity of spreadsheet software in enterprise environments and the potential for weaponized documents to bypass standard perimeter security controls.\nNo special authentication or elevated privileges are required by the attacker prior to exploitation, although local access or user interaction in the form of opening the malicious file is necessary to trigger the parsing flaw.",
  "technicalDetails": "The vulnerability is classified as an out-of-bounds read, stemming from improper bounds checking within the Microsoft Office Excel file parsing engine when processing specific record structures inside spreadsheet documents.\nThe root cause lies in the application's failure to adequately validate the size and offset parameters specified within the file format structures against the actual allocated buffer boundaries. When Microsoft Office Excel processes a malformed file containing manipulated length descriptors, the internal parsing routines attempt to read data from memory locations outside the designated buffer boundaries.\nExploitation occurs through a step-by-step attack flow. First, an unauthorized attacker crafts a malicious spreadsheet file containing corrupted or maliciously altered record lengths. Second, the adversary delivers this file to the target victim via email, removable media, or network shares. Third, the victim opens the crafted file using a vulnerable version of Microsoft Office Excel. Fourth, upon parsing the malicious structures, the application triggers the out-of-bounds read condition. Fifth, this memory mismanagement corrupts adjacent heap or stack structures, allowing the attacker to manipulate program execution flow and achieve arbitrary code execution.\nThe vulnerable component is the file parser module within Microsoft Office Excel responsible for interpreting legacy or modern spreadsheet formats. The vulnerability operates locally and does not require network exposure for the initial trigger. Authentication is not required, but exploitation depends on local execution and user interaction to open the malicious file.\nPost-exploitation impact includes the execution of arbitrary payloads with the privileges of the logged-on user. An attacker can leverage this execution state to install persistent malware, access sensitive documents, harvest credentials, or pivot to other systems within the internal network."
}