CVE-2026-68807: Microsoft 365 Apps Buffer Overflow Flaw

CVE-2026-68807 Overview

CVE-2026-68807 is a heap-based buffer overflow vulnerability in Microsoft Office Excel that allows an unauthorized attacker to execute code locally. The flaw is tracked under CWE-122 and affects multiple supported Office releases, including Microsoft 365 Apps, Office 2019, Office 2021, and Office 2024 across Windows and macOS. Exploitation requires user interaction, typically opening a crafted Excel document. Successful exploitation yields code execution in the context of the current user, enabling attackers to install programs, modify data, or create new accounts.

Critical Impact
An attacker who successfully exploits this vulnerability can execute arbitrary code on the target system with the privileges of the user opening a malicious Excel file.

Affected Products

Microsoft 365 Apps (Enterprise, x64 and x86)
Microsoft Excel 2016, Microsoft Office 2019, Office 2021 LTSC, Office 2024 LTSC
Microsoft 365 and Office LTSC on macOS

Discovery Timeline

2026-08-11 - CVE-2026-68807 published to NVD
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-68807

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow in the Excel file parsing logic. When Excel processes a specially crafted spreadsheet, a length or size value is trusted without proper validation, causing more data to be written to a heap buffer than allocated. The adjacent heap metadata and object pointers become attacker-controlled, opening the path to arbitrary code execution.

The attack vector is local and requires user interaction. An attacker delivers a malicious .xls, .xlsx, or related Office document through email, a shared drive, or a web download. Once the user opens the file, parsing triggers the overflow and code executes with the current user's privileges. No prior authentication to the target system is required beyond the interaction of the victim.

With an EPSS probability of 0.303%, public exploitation activity has not been observed at the time of publication, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The root cause is improper bounds checking on heap-allocated buffers during the parsing of structured spreadsheet content. Attacker-supplied fields within the document control the copy length used against a fixed-size heap allocation. See the Microsoft Security Response Center advisory for vendor-specific details.

Attack Vector

Exploitation follows a standard client-side document attack pattern. The attacker crafts a malicious Excel document containing manipulated record structures. The document is delivered via phishing email, malicious website, or file share. When the victim opens the file in an affected Excel version, the parser triggers the heap overflow. Code executes in the security context of the user, and the attacker can then perform post-exploitation actions such as credential theft, persistence installation, or lateral movement.

No verified proof-of-concept code has been released. Refer to the vendor advisory for technical detail.

Detection Methods for CVE-2026-68807

Indicators of Compromise

Unexpected Excel processes (EXCEL.EXE) spawning child processes such as cmd.exe, powershell.exe, rundll32.exe, or wscript.exe.
Excel writing executable content to disk in user-writable paths such as %APPDATA%, %TEMP%, or %LOCALAPPDATA%.
Anomalous outbound network connections initiated by Excel to previously unseen domains or IP addresses shortly after a document is opened.
Crash telemetry for Excel referencing heap corruption or access violations during file open operations.

Detection Strategies

Hunt for Office parent-child process anomalies using EDR telemetry, focusing on Excel spawning scripting or LOLBin binaries.
Correlate email gateway detections of Excel attachments with subsequent endpoint process execution to identify weaponized documents.
Monitor for module loads of unusual DLLs by EXCEL.EXE outside standard Office installation directories.

Monitoring Recommendations

Enable and forward Microsoft Defender for Office 365 or equivalent mail security logs to a centralized SIEM for retention and correlation.
Ingest Sysmon Event ID 1 (process creation) and Event ID 11 (file created) for Office applications into your data lake.
Track Excel crash and Windows Error Reporting events on endpoints to surface exploitation attempts that fail before payload execution.

How to Mitigate CVE-2026-68807

Immediate Actions Required

Apply the security update referenced in the Microsoft CVE-2026-68807 Advisory to all affected Office installations.
Prioritize patching endpoints belonging to users with elevated privileges or access to sensitive data.
Block Excel documents from untrusted sources at the mail gateway and enforce Protected View for files originating from the internet.

Patch Information

Microsoft has released updates for Microsoft 365 Apps, Excel 2016, Office 2019, Office 2021 LTSC, and Office 2024 LTSC on both Windows and macOS. Deploy the fix through Microsoft Update, Microsoft 365 Apps Update Channel, or your standard patch management workflow. Confirm remediation by validating build numbers against the vendor advisory.

Workarounds

Enforce Office Protected View and Application Guard for documents from the internet and other untrusted locations.
Configure Attack Surface Reduction (ASR) rules to block Office applications from creating child processes and from injecting code into other processes.
Restrict macro execution and disable legacy file formats where operationally feasible until patches are applied.

bash

# Example: enable relevant Microsoft Defender ASR rules via PowerShell
Add-MpPreference -AttackSurfaceReductionRules_Ids `
  D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
  -AttackSurfaceReductionRules_Actions Enabled

Add-MpPreference -AttackSurfaceReductionRules_Ids `
  75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 `
  -AttackSurfaceReductionRules_Actions Enabled