CVE-2026-45463: Microsoft Office Buffer Overflow Flaw

CVE-2026-45463 Overview

CVE-2026-45463 is a heap-based buffer overflow vulnerability in Microsoft Office that allows an unauthorized attacker to execute code locally. The flaw maps to [CWE-121: Stack-based Buffer Overflow] in the NVD record, with the description identifying heap memory corruption as the root condition. The vulnerability carries a CVSS 3.1 base score of 8.4 and requires no privileges or user interaction at the time of exploitation. Successful exploitation results in full compromise of confidentiality, integrity, and availability on the local system. Microsoft has published advisory details in the Microsoft CVE-2026-45463 Update Guide.

Critical Impact
An attacker who successfully exploits this vulnerability can execute arbitrary code locally with the privileges of the user running Microsoft Office, leading to full system compromise.

Affected Products

Microsoft Office (specific build numbers listed in the Microsoft Security Update Guide)
Refer to the Microsoft CVE-2026-45463 Update Guide for the authoritative list of affected SKUs and versions

Discovery Timeline

2026-06-09 - CVE-2026-45463 published to NVD
2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-45463

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow within Microsoft Office. An attacker crafts a malicious Office document that, when processed by the application, writes data past the bounds of a heap-allocated buffer. The corrupted heap region overlaps with adjacent allocations or control structures used by the Office process. Manipulating these structures lets the attacker redirect execution into attacker-controlled code. Because the attack vector is local, exploitation typically requires the victim to open the malicious file. The exploit prediction score from EPSS is low at the time of publication, but the impact profile remains severe across confidentiality, integrity, and availability.

Root Cause

The root cause is improper validation of data length or structure before copying input into a heap-allocated buffer in Microsoft Office. When Office parses a specially crafted document, the routine writes more bytes than the destination buffer can hold. This corrupts adjacent heap metadata or object pointers used later by the application.

Attack Vector

An attacker delivers a malicious Office document through email, file share, or web download. The victim opens the file in a vulnerable version of Microsoft Office. Parsing the document triggers the heap overflow, allowing the attacker to hijack control flow and execute arbitrary code in the context of the current user. No prior authentication is required, and the vulnerability is exploited entirely on the local endpoint.

The NVD entry does not publish proof-of-concept code, and no public exploit is currently listed in Exploit-DB. Technical specifics are restricted to the Microsoft CVE-2026-45463 Update Guide.

Detection Methods for CVE-2026-45463

Indicators of Compromise

Unexpected child processes spawned from winword.exe, excel.exe, or powerpnt.exe, such as cmd.exe, powershell.exe, or rundll32.exe
Office processes writing executable files to user-writable directories like %APPDATA%, %TEMP%, or %LOCALAPPDATA%
Crash dumps or Windows Error Reporting events for Office binaries citing heap corruption or access violations
Outbound network connections originating from Office processes to unfamiliar external hosts following document open events

Detection Strategies

Hunt for anomalous parent-child process relationships where Office applications launch scripting interpreters or LOLBins
Inspect Office documents arriving via email gateways for embedded objects, OLE streams, and unusual macros or external data references
Correlate document open telemetry with subsequent file write, registry modification, or persistence events on the same host
Apply YARA rules targeting malformed structures in Office formats once Microsoft publishes signature guidance

Monitoring Recommendations

Forward EDR process, file, and network telemetry from all endpoints running Microsoft Office to a centralized analytics platform
Enable Microsoft Defender Attack Surface Reduction rules that block Office child processes and Office injection into other processes
Monitor Windows Event Logs for application crashes in Office binaries, which can indicate exploitation attempts or unstable payloads
Track patch deployment status across the estate using vulnerability management tooling to confirm coverage

How to Mitigate CVE-2026-45463

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-45463 Update Guide as soon as it is available in your change window
Block or quarantine inbound Office documents from untrusted sources at email and web gateways until patching is complete
Enforce Protected View and Block Macros from the Internet for all Microsoft Office installations
Restrict local administrator rights so that successful exploitation runs under a least-privileged user account

Patch Information

Microsoft has issued guidance and updates through the Microsoft Security Response Center. Administrators should consult the Microsoft CVE-2026-45463 Update Guide for the precise KB articles, affected builds, and fixed versions. Deploy updates through Microsoft Update, WSUS, Intune, or Configuration Manager according to your patching policy.

Workarounds

Enable Attack Surface Reduction rules to block child process creation by Office applications
Configure Office to open files from the internet and email attachments in Protected View by default
Disable preview pane handlers for Office formats in Outlook and Windows Explorer to prevent automatic parsing
Use Application Control or Windows Defender Application Control to restrict execution of unsigned binaries spawned from Office processes

bash

# Example: enable ASR rule to block Office apps from creating child processes
Set-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled