CVE-2026-69614: Microsoft 365 Apps Buffer Overflow Flaw

CVE-2026-69614 Overview

CVE-2026-69614 is a stack-based buffer overflow vulnerability in Microsoft Office Access that allows an unauthorized attacker to execute arbitrary code over a network. The flaw affects multiple Microsoft Office product lines, including Microsoft 365 Apps, Access 2016, Office 2019, Office 2021 LTSC, and Office 2024 LTSC. Successful exploitation requires user interaction, typically opening a crafted Access database file delivered through email or a compromised website. The vulnerability maps to [CWE-20] Improper Input Validation and enables full compromise of confidentiality, integrity, and availability on affected hosts.

Critical Impact
An attacker who successfully exploits CVE-2026-69614 can execute code in the security context of the current user, enabling malware installation, data theft, and lateral movement across enterprise Office deployments.

Affected Products

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

Discovery Timeline

2026-09-08 - CVE-2026-69614 published to NVD
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-69614

Vulnerability Analysis

CVE-2026-69614 is a stack-based buffer overflow in Microsoft Office Access. The parser responsible for handling Access database structures writes attacker-controlled data past the bounds of a fixed-size stack buffer. This overwrite corrupts adjacent stack memory, including saved return addresses and stack frame metadata, which an attacker can use to redirect execution to attacker-supplied code.

Exploitation runs with the privileges of the user opening the malicious file. On workstations where users hold local administrator rights, this yields immediate host compromise. The vulnerability affects both Click-to-Run Microsoft 365 Apps and traditional MSI installations across Office 2016 through Office 2024.

Root Cause

The root cause is improper input validation ([CWE-20]) during processing of Access file content. The application fails to enforce length constraints before copying attacker-supplied fields into a stack buffer. The absence of a bounds check enables the overflow that leads to control-flow hijack.

Attack Vector

The attack vector is network-based with required user interaction. A common delivery pattern involves emailing a crafted .accdb or .mdb file, or hosting one on a website that the target opens. Once the victim opens the file in Access or an Office component that renders Access data, the vulnerable code path triggers and the attacker gains code execution. No prior authentication to the target system is required.

No verified proof-of-concept code is publicly available at the time of writing. Consult the Microsoft CVE-2026-69614 Update Guide for authoritative technical detail.

Detection Methods for CVE-2026-69614

Indicators of Compromise

Unexpected MSACCESS.EXE child processes such as cmd.exe, powershell.exe, rundll32.exe, or regsvr32.exe.
Access database files (.accdb, .mdb, .accde) arriving via email attachments or downloads from untrusted domains.
Crashes of MSACCESS.EXE logged in the Windows Application event log with exception codes indicating stack corruption.
Outbound network connections initiated by MSACCESS.EXE to unfamiliar external hosts shortly after a file open event.

Detection Strategies

Hunt for process creation events where MSACCESS.EXE spawns scripting or LOLBAS binaries, which is atypical for normal database use.
Correlate email gateway telemetry with endpoint file-write events for Access file extensions to identify targeted delivery.
Monitor for suspicious module loads inside Office processes, including unsigned DLLs and reflectively loaded code.

Monitoring Recommendations

Enable Microsoft Defender Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and injecting into other processes.
Forward Office and Sysmon telemetry to a centralized analytics platform for behavioral correlation across users.
Alert on any Access process performing network egress to non-corporate destinations.

How to Mitigate CVE-2026-69614

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-69614 Update Guide to all affected Office installations.
Prioritize patching for users who routinely handle external Access databases, including finance, HR, and administrative staff.
Block inbound .accdb, .mdb, and .accde attachments at the email gateway unless a documented business need exists.
Enforce Protected View and Mark-of-the-Web handling for files originating from the internet.

Patch Information

Microsoft has released updates addressing CVE-2026-69614 across Microsoft 365 Apps, Access 2016, Office 2019, Office 2021 LTSC, and Office 2024 LTSC. Click-to-Run deployments receive fixes through the standard Office update channel, while MSI-based installations require the corresponding security update package. Verify the installed build against the fixed versions listed in the vendor advisory.

Workarounds

Configure Office File Block policy to prevent opening legacy Access file formats from untrusted locations.
Deploy ASR rule 26190899-1602-49e8-8b27-eb1d0a1ce869 (Block Office communication applications from creating child processes) and related Office ASR rules.
Restrict Access usage to specific business units via application control policies until patching completes.

bash

# Enable ASR rule to block Office child process creation (PowerShell, run as admin)
Set-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled

# Block legacy Access file formats via registry (per-user example for Access 2016)
reg add "HKCU\Software\Microsoft\Office\16.0\Access\Security\FileBlock" /v "AccessDB" /t REG_DWORD /d 2 /f