CVE-2026-108435: Microsoft 365 Apps Information Disclosure

CVE-2026-108435 Overview

CVE-2026-108435 is an untrusted pointer dereference vulnerability [CWE-822] in Microsoft Office Word. The flaw allows an unauthorized remote attacker to disclose sensitive information when a user opens a crafted document. Exploitation requires user interaction, such as opening a malicious Word file delivered through email or a web download. The vulnerability affects multiple supported Office releases, including Microsoft 365 Apps, Office 2021, and Office 2024 across Windows and macOS platforms. Microsoft published the advisory in its Security Update Guide and has released patches through its monthly servicing channels.

Critical Impact
Successful exploitation discloses memory contents from the Word process, potentially exposing document data, credentials, or address-space information useful for chaining further attacks.

Affected Products

Microsoft 365 Apps (x86 and x64 enterprise editions)
Microsoft Office LTSC 2021 (Windows and macOS)
Microsoft Office LTSC 2024 (Windows and macOS)

Discovery Timeline

2026-10-15 - CVE-2026-108435 published to the National Vulnerability Database
2026-10-20 - NVD record last modified

Technical Details for CVE-2026-108435

Vulnerability Analysis

The vulnerability resides in how Microsoft Word parses structured document data. During processing, Word dereferences a pointer whose value is derived from attacker-controlled input in a crafted document. Because the pointer is not validated before use, the parser reads memory from an address chosen by the attacker.

The resulting read exposes process memory back through document rendering state, embedded field values, or error paths. An attacker uses this primitive to leak sensitive data from the Word process address space. The confidentiality impact is high, while integrity and availability are unaffected per the CVSS vector.

Exploitation is network-reachable because malicious documents are typically delivered via email attachments, SharePoint links, Teams channels, or web downloads. The vulnerability requires user interaction: a target must open the file. No privileges or prior authentication to the victim system are required.

Root Cause

The root cause maps to CWE-822: Untrusted Pointer Dereference. The parser trusts a pointer value, offset, or object reference supplied inside the document file format without validating that it points to a legitimate, in-bounds allocation. When the code reads from that address, it treats arbitrary memory as a valid object field.

Attack Vector

An attacker crafts a Word document containing malformed structures that steer the vulnerable parser toward an attacker-chosen pointer value. The attacker delivers the file through phishing, drive-by download, or a trusted collaboration channel. On open, Word dereferences the pointer and surfaces disclosed memory contents, which the attacker retrieves either directly in rendered output or by exfiltrating state the document can observe.

No verified exploit code is publicly available at the time of writing. Refer to the Microsoft Security Update Guide for vendor technical details.

Detection Methods for CVE-2026-108435

Indicators of Compromise

Inbound email attachments containing .docx, .doc, .docm, or .rtf files from unverified senders, especially with malformed OOXML structures or unusual embedded objects.
Office child processes spawning unexpected binaries such as powershell.exe, wscript.exe, or rundll32.exe immediately after document open.
Outbound network connections initiated by winword.exe to uncategorized or newly registered domains shortly after a document is opened.

Detection Strategies

Hunt for Word process crashes or exception events referencing access violations in document parsing modules on endpoints running unpatched Office builds.
Correlate email gateway telemetry with endpoint document-open events to identify suspicious document delivery followed by anomalous Word behavior.
Apply YARA or content inspection rules to flag Office documents containing malformed object structures consistent with pointer-dereference triggers.

Monitoring Recommendations

Monitor winword.exe for anomalous memory access patterns, module loads, and outbound DNS or HTTP activity using EDR telemetry.
Track Office application version inventory to confirm all endpoints are on patched builds published after the October 2026 Microsoft security release.
Review Microsoft Defender for Office 365 or equivalent email security logs for blocked or quarantined Word documents linked to targeted campaigns.

How to Mitigate CVE-2026-108435

Immediate Actions Required

Apply the Microsoft Office security updates referenced in the Microsoft Security Update Guide across all affected Microsoft 365 Apps, Office 2021, and Office 2024 installations.
Validate that Click-to-Run and Microsoft Update channels have delivered the latest Office build to managed endpoints, including macOS devices.
Enforce Protected View and Office Trust Center settings so that documents from the internet and email attachments open in a sandboxed state.

Patch Information

Microsoft released fixes through its standard Office servicing channels. Administrators should consult the Microsoft Security Update Guide for the exact build numbers corresponding to Microsoft 365 Apps, Office LTSC 2021, and Office LTSC 2024 on Windows and macOS. Patch deployment should be prioritized for user populations with heavy external document exposure.

Workarounds

Block or quarantine inbound Word document formats at the email gateway for high-risk user groups until patches are deployed.
Enforce the Office Block macros from running in Office files from the Internet policy and keep Protected View enabled for files from untrusted locations.
Use Attack Surface Reduction rules to prevent Office applications from creating child processes and injecting into other processes.

bash

# Example: enforce Protected View via Group Policy registry keys (Windows)
reg add "HKCU\Software\Policies\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableAttachmentsInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Policies\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Policies\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f