CVE-2026-55050 Overview
CVE-2026-55050 is an out-of-bounds read vulnerability [CWE-125] in Microsoft Office Word that allows a local, unauthorized attacker to disclose sensitive information. Exploitation requires user interaction, typically opening a crafted document. The flaw affects a broad set of Microsoft Office products, including Microsoft 365 Apps, Office 2019, Office 2021, Office 2024, Office Online Server, SharePoint Server, and Word 2016. Successful exploitation exposes process memory contents that may include sensitive user data or values useful for chaining further attacks.
Critical Impact
An attacker who convinces a user to open a malicious Word document can read out-of-bounds memory and disclose confidential information processed by Word.
Affected Products
- Microsoft 365 Apps (Enterprise x64/x86), Microsoft 365 for macOS
- Microsoft Office 2019, Office 2021 (LTSC and macOS), Office 2024 (LTSC and macOS)
- Microsoft Word 2016, Office Online Server, SharePoint Server 2016/2019/Subscription Edition
Discovery Timeline
- 2026-07-14 - CVE-2026-55050 published to NVD
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-55050
Vulnerability Analysis
The vulnerability is an out-of-bounds read [CWE-125] within Microsoft Office Word's document parsing logic. When Word processes a specially crafted file, the parser reads memory beyond the boundaries of an allocated buffer. This exposes adjacent memory contents to the attacker-controlled processing path. The disclosed data can be exfiltrated through document fields, embedded content, or observable rendering behavior. The vulnerability has no impact on integrity or availability, only confidentiality. Attackers frequently combine such information disclosure flaws with memory corruption bugs to bypass Address Space Layout Randomization (ASLR) during exploit development.
Root Cause
The root cause is missing or insufficient bounds checking when Word parses structured content within a document. A malformed field, record length, or offset causes the parser to read past the end of an allocated buffer without validating the read range against the buffer's declared size.
Attack Vector
Exploitation requires local access with user interaction. An attacker crafts a malicious Word document and delivers it through email, a file share, or a web download. When the user opens the document in a vulnerable Office application, the parser triggers the out-of-bounds read. No elevated privileges are required, and the attack executes in the user's context. See the Microsoft Security Update CVE-2026-55050 advisory for vendor technical details.
// No verified proof-of-concept code is available for CVE-2026-55050.
// Refer to the Microsoft Security Response Center advisory for details.
Detection Methods for CVE-2026-55050
Indicators of Compromise
- Word documents (.doc, .docx, .rtf) received from untrusted sources, especially those with malformed structures or unusual field codes.
- Office application crashes or unexpected exceptions in WINWORD.EXE correlated with opening specific documents.
- Outbound network connections initiated from WINWORD.EXE immediately after a document is opened, indicating potential exfiltration of disclosed memory.
Detection Strategies
- Inspect inbound email attachments and file shares with sandbox detonation to observe abnormal Word parsing behavior.
- Enable Attack Surface Reduction (ASR) rules that block Office child process creation and suspicious behaviors.
- Correlate telemetry from endpoint detection tools to flag Office processes reading unusual memory regions or spawning script interpreters.
Monitoring Recommendations
- Monitor process creation events for WINWORD.EXE invoking powershell.exe, cmd.exe, or mshta.exe.
- Track file creation of Office documents from browsers and mail clients into user profile directories.
- Alert on Office applications establishing outbound HTTPS connections to newly observed or low-reputation domains.
How to Mitigate CVE-2026-55050
Immediate Actions Required
- Apply Microsoft's July 2026 security updates for all affected Office and SharePoint products as documented in the MSRC advisory.
- Inventory endpoints running Microsoft 365 Apps, Office 2016/2019/2021/2024, Office Online Server, and SharePoint Server to confirm patch coverage.
- Enforce Protected View and Block macros from running in Office files from the Internet through Group Policy.
Patch Information
Microsoft has released security updates addressing CVE-2026-55050 across affected products. Refer to the Microsoft Security Update CVE-2026-55050 guidance for the specific KB articles and channel builds applicable to each product SKU.
Workarounds
- Open untrusted Word documents only in Protected View or in a sandboxed viewer.
- Use the File Block Policy in Office to restrict opening of legacy Word file formats from untrusted locations.
- Deploy Microsoft Defender Application Guard for Office to isolate untrusted documents from the host operating system.
# Enable Protected View for files originating from the Internet (Group Policy registry key)
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 DisableAttachmentsInPV /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
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
