Description

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

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.5",
  "pubDate": "2026-08-11T17:19:05.563Z",
  "pubdate": "2026-08-11T17:19:05.563Z",
  "executiveSummary": "An out-of-bounds read vulnerability exists in Microsoft Office Excel, which allows an unauthorized attacker to disclose sensitive local information.\nThe vulnerability type is classified as an out-of-bounds read, stemming from improper input validation or boundary checking during the parsing of maliciously crafted spreadsheet files.\nThe primary impact of this flaw is unauthorized information disclosure, potentially exposing sensitive memory contents or local data to an adversary.\nAffected systems include deployments of Microsoft Office Excel that process untrusted spreadsheet files.\nThe risk implications involve the potential leakage of critical process memory, which could be leveraged by attackers in conjunction with other vulnerabilities to bypass security mitigations such as Address Space Layout Randomization (ASLR).\nAttacker capabilities are constrained to local information disclosure; the vulnerability does not inherently provide remote code execution or direct write capabilities based on the provided data.\nExploitation requirements dictate that an unauthorized attacker must trick a user into opening a specially crafted Excel file locally, or otherwise induce the vulnerable application to process malicious file input.",
  "technicalDetails": "The vulnerability resides within the file parsing and memory management components of Microsoft Office Excel responsible for handling proprietary or open spreadsheet formats.\nThe root cause of the out-of-bounds read is a failure in the application logic to properly validate boundary constraints and size parameters when reading data structures from a file into internal memory buffers.\nThe vulnerable component involves the internal parser functions tasked with interpreting specific records or streams within Excel documents.\nAffected versions encompass instances of Microsoft Office Excel that lack the necessary security updates to correct boundary verification checks.\nAuthentication requirements are nonexistent for the initial trigger, as the attack relies on processing static file data rather than authenticated network sessions.\nPrivilege requirements are minimal; the attacker requires only the standard user privileges necessary to execute the application and open a malicious file locally.\nNetwork exposure is not strictly required for exploitation, as the vulnerability manifests locally during file rendering, though files could theoretically be delivered via email or web downloads.\nThe payload behavior involves the construction of a malformed spreadsheet containing intentionally manipulated header fields, length descriptors, or offset values that mismatch the actual payload size.\nWhen Microsoft Office Excel processes the malicious file, the internal parsing routines read past the allocated buffer boundaries due to the unchecked offset values.\nThe post-exploitation impact centers on local information disclosure, wherein adjacent memory contents are read and potentially echoed back through application behavior, error logs, or memory dumping mechanisms accessible to the process.\nStep-by-step exploitation occurs as follows: first, the attacker crafts a malicious Excel file with modified structural dimensions or stream sizes; second, the victim opens the file using a vulnerable version of Microsoft Office Excel; third, the application parses the corrupted fields without proper bounds checking; fourth, the parsing engine reads out-of-bounds memory locations into application buffers; and finally, the leaked memory contents are leveraged by the attacker to harvest sensitive data or assist in advanced multi-stage exploitation."
}