CVE-2026-64919: MS Office Access Buffer Overflow Flaw

CVE-2026-64919 Overview

CVE-2026-64919 is a stack-based buffer overflow vulnerability in Microsoft Office Access. An unauthorized attacker can execute code locally on a target system by convincing a user to open a crafted Access file. The flaw is tracked under CWE-121 (Stack-based Buffer Overflow) and carries a CVSS 3.1 score of 7.8. Exploitation requires local access and user interaction, but no prior privileges. Successful exploitation results in high impact to confidentiality, integrity, and availability. Microsoft published the advisory on 2026-08-11.

Critical Impact
Successful exploitation grants an attacker arbitrary code execution in the context of the current user, enabling installation of programs, data theft, and account takeover on the local host.

Affected Products

Microsoft Office Access (see the Microsoft CVE-2026-64919 Advisory for the definitive product and build list)
Specific affected versions were not enumerated in the NVD entry at publication
Refer to the vendor advisory for authoritative CPE data

Discovery Timeline

2026-08-11 - CVE-2026-64919 published to NVD
2026-08-12 - Last updated in NVD database

Technical Details for CVE-2026-64919

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow [CWE-121] within Microsoft Office Access. Access writes attacker-controlled data past the bounds of a fixed-size stack buffer while parsing a crafted database or object structure. Overflowing the buffer corrupts adjacent stack memory, including the saved return address and structured exception handler records. An attacker who controls the overflowing content can redirect execution to attacker-supplied instructions.

Because the attack vector is local and requires user interaction, exploitation is typically delivered through a malicious .accdb, .mdb, or related Access file. The file may arrive by email, download, or shared network location. Opening the crafted file in a vulnerable Access build triggers the parser path that leads to the overflow. The EPSS score at publication is 0.31%, reflecting low observed exploitation activity so far.

Root Cause

The root cause is missing or incorrect bounds validation in a routine that copies structured file content into a stack-allocated buffer. When the input length exceeds the destination size, the copy proceeds and corrupts stack frames. Microsoft has not disclosed the specific function or parser component in public materials.

Attack Vector

An attacker crafts a malicious Access file and delivers it to a target user. The victim opens the file with a vulnerable version of Access. During parsing, the oversized field overflows the stack buffer and hijacks control flow. The resulting code executes with the privileges of the user running Access. No authentication is required on the target beyond the user opening the file. See the Microsoft CVE-2026-64919 Advisory for vendor-supplied exploitation notes.

// No verified public proof-of-concept is available.
// Refer to the Microsoft advisory for authoritative technical details.

Detection Methods for CVE-2026-64919

Indicators of Compromise

Unexpected child processes spawned by MSACCESS.EXE, particularly cmd.exe, powershell.exe, rundll32.exe, or regsvr32.exe
Access opening .accdb, .mdb, .accde, or .mde files from email attachments, browser download folders, or untrusted network shares
Crash events or Windows Error Reporting entries referencing MSACCESS.EXE with stack corruption signatures

Detection Strategies

Alert on Office applications writing executables or scripts to disk in user-writable paths such as %TEMP%, %APPDATA%, or %PUBLIC%
Correlate Access process launches with subsequent network connections to unfamiliar external hosts
Hunt for Office parent processes invoking living-off-the-land binaries such as mshta.exe, wscript.exe, or bitsadmin.exe

Monitoring Recommendations

Enable Microsoft Defender Attack Surface Reduction rules that block Office child process creation and executable content from email
Ingest Sysmon process creation, image load, and file write events into a central SIEM for retrospective hunting
Track Office telemetry for anomalous file opens originating from Mark-of-the-Web tagged sources

How to Mitigate CVE-2026-64919

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-64919 Advisory to all systems running Microsoft Office Access
Inventory endpoints with Access installed and prioritize patching for users who routinely handle external database files
Block inbound .accdb, .mdb, .accde, and .mde attachments at the mail gateway until patching is complete

Patch Information

Microsoft has released a security update addressing this vulnerability. Consult the Microsoft CVE-2026-64919 Advisory for the specific KB article, affected builds, and fixed versions applicable to your Office channel (Current Channel, Monthly Enterprise Channel, or Semi-Annual Enterprise Channel).

Workarounds

Enforce Protected View and Office File Block policy to prevent legacy Access file formats from opening directly
Configure Group Policy to disable macros and ActiveX in Office documents originating from the internet
Restrict Access installations to users with a documented business need until updates are deployed

bash

# No configuration workaround is published by the vendor.
# Follow the Microsoft advisory guidance and apply the security update.