CVE-2026-108447 Overview
CVE-2026-108447 is a heap-based buffer overflow vulnerability in Microsoft Office Word that enables remote code execution. An unauthorized attacker can execute arbitrary code over a network when a user opens a crafted document. The flaw is tracked under CWE-122 and affects Microsoft 365 Apps, Microsoft Office 2021 LTSC, and Microsoft Office 2024 LTSC on both x64 and x86 platforms. Microsoft published the advisory on October 15, 2026.
Critical Impact
Successful exploitation results in arbitrary code execution in the context of the logged-on user, with high impact to confidentiality, integrity, and availability.
Affected Products
- Microsoft 365 Apps (Enterprise, x64 and x86)
- Microsoft Office 2021 LTSC (x64 and x86)
- Microsoft Office 2024 LTSC (x64 and x86)
Discovery Timeline
- 2026-10-15 - Microsoft published advisory for CVE-2026-108447
- 2026-10-15 - CVE-2026-108447 published to NVD
- 2026-10-19 - Last updated in NVD database
Technical Details for CVE-2026-108447
Vulnerability Analysis
The vulnerability is a heap-based buffer overflow [CWE-122] in the Microsoft Office Word document parsing logic. Word allocates a heap buffer based on size metadata embedded in a document structure. When the parser copies data into that buffer, it fails to enforce the allocated boundary. Attacker-controlled bytes then overwrite adjacent heap memory, including object headers, function pointers, or control structures used by Word.
An attacker who shapes the heap layout before the overflow can redirect execution to attacker-supplied code. The resulting code runs with the privileges of the current Office user, giving the attacker read, write, and execute access to anything that user controls.
Root Cause
The root cause is improper validation of a length or offset field during parsing of a Word document element. The parser trusts the field without verifying that the destination buffer can hold the resulting data. This mismatch between declared size and allocated size produces the overflow condition.
Attack Vector
Exploitation requires a user to open a weaponized .doc, .docx, or related Office document. Delivery is network-based through email attachments, phishing links, SharePoint, OneDrive, or compromised web pages that host the file. The Preview Pane may also serve as an attack surface for Office document renderers, broadening the exposure.
No authentication is required against the target system. User interaction is limited to opening the file, which is routine behavior in most enterprise workflows.
No verified public proof-of-concept code is available at this time. See the Microsoft CVE-2026-108447 Advisory for vendor technical details.
Detection Methods for CVE-2026-108447
Indicators of Compromise
- Unexpected child processes spawned by winword.exe, such as cmd.exe, powershell.exe, rundll32.exe, or mshta.exe.
- Outbound network connections initiated by winword.exe to untrusted or newly registered domains shortly after document open.
- Office document files arriving via email with obfuscated content, embedded objects, or anomalous OLE streams.
- Crash events or Windows Error Reporting entries referencing winword.exe with heap corruption signatures.
Detection Strategies
- Deploy behavioral detections for Office applications executing scripting engines, LOLBins, or writing executable content to disk.
- Correlate document open events with subsequent process creation and network telemetry to identify exploitation chains.
- Alert on winword.exe loading unexpected modules or allocating executable heap regions.
Monitoring Recommendations
- Ingest Microsoft Defender, Sysmon, and EDR process telemetry into a central SIEM for cross-host correlation.
- Track email gateway logs for Office attachments from external senders and apply sandbox detonation.
- Monitor Office telemetry channels, including Protected View bypass events and macro execution attempts.
How to Mitigate CVE-2026-108447
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-108447 Advisory to all affected Office installations.
- Prioritize patch deployment on endpoints that handle external documents, including executive assistants, finance, and HR workstations.
- Verify Microsoft 365 Apps update channels are current and not pinned to a vulnerable build.
- Block or quarantine inbound Office documents from untrusted senders at the mail gateway until patching is confirmed.
Patch Information
Microsoft issued the fix through the standard Office servicing channels for Microsoft 365 Apps, Office 2021 LTSC, and Office 2024 LTSC. Administrators should confirm installed build numbers against the vendor advisory for each SKU and architecture (x64 and x86). Refer to the Microsoft CVE-2026-108447 Advisory for the authoritative patch matrix.
Workarounds
- Enforce Protected View and Office Protected View for files originating from the internet and email attachments.
- Disable the Outlook Preview Pane for untrusted mailboxes to reduce passive rendering exposure.
- Apply Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and injecting into other processes.
- Enforce signed-macros-only policy and block macros from the internet via Group Policy.
# Example: enable ASR rule blocking Office child processes via PowerShell
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A -AttackSurfaceReductionRules_Actions Enabled
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
