CVE-2026-64917 Overview
CVE-2026-64917 is an out-of-bounds read vulnerability [CWE-125] in Microsoft Office Word. An unauthorized attacker can exploit the flaw to disclose information locally after convincing a user to open a crafted document. The vulnerability requires user interaction and local access, limiting remote exploitation scenarios.
Successful exploitation exposes memory contents that may include sensitive data adjacent to the affected buffer. The vulnerability does not affect integrity or availability, only confidentiality of process memory.
Critical Impact
Attackers who deliver a malicious Word document can read out-of-bounds memory and disclose sensitive information from the process address space.
Affected Products
- Microsoft Office Word (specific versions listed in the Microsoft CVE-2026-64917 Advisory)
Discovery Timeline
- 2026-08-11 - CVE-2026-64917 published to NVD
- 2026-08-11 - Last updated in NVD database
Technical Details for CVE-2026-64917
Vulnerability Analysis
The vulnerability is an out-of-bounds read in Microsoft Office Word's document parsing logic. When Word processes a specially crafted file, the application reads memory beyond the bounds of an allocated buffer. The read operation returns data from adjacent memory regions to the parsing routine.
The attack vector is local and requires user interaction. An attacker must deliver the crafted document to the victim and convince them to open it in Word. No elevated privileges are required to trigger the condition.
The impact is limited to information disclosure. Attackers cannot directly modify memory or crash the process through this flaw alone. However, disclosed memory may contain pointers, tokens, or document data useful for chaining with other vulnerabilities.
Root Cause
The root cause is missing or incorrect bounds validation during structured data parsing in Word. The parser trusts length or offset fields from the document without confirming they fall within allocated buffer boundaries. This mirrors the general [CWE-125] pattern of reading past the end of an intended memory region.
Attack Vector
Exploitation requires an attacker to craft a malicious Word document containing manipulated structural fields that trigger the out-of-bounds read. The attacker delivers the document via phishing email, file share, or web download. When the victim opens the file, Word parses the malformed data and reads beyond the intended buffer. Disclosed memory content can then be exfiltrated through embedded content or observed via error behavior. Technical details are limited pending vendor disclosure; refer to the Microsoft CVE-2026-64917 Advisory for authoritative information.
Detection Methods for CVE-2026-64917
Indicators of Compromise
- Unexpected .docx, .doc, or .rtf files received from untrusted senders or unusual internal sources.
- Word process (WINWORD.EXE) crashes, hangs, or anomalous memory access patterns after opening a document.
- Outbound network connections initiated by WINWORD.EXE immediately after document open.
Detection Strategies
- Inspect email attachments and downloaded documents with sandbox detonation to identify malformed Word files that trigger parser anomalies.
- Monitor endpoint telemetry for WINWORD.EXE spawning child processes or accessing sensitive files immediately after opening a document.
- Correlate document open events with unusual memory faults or crash reports on user workstations.
Monitoring Recommendations
- Enable Microsoft Office telemetry and forward crash dumps and Application event logs to a central SIEM.
- Track document provenance using Mark-of-the-Web and Protected View events.
- Alert on Word processes reading unusual memory regions or exhibiting abnormal handle counts.
How to Mitigate CVE-2026-64917
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-64917 Advisory as soon as it is available in your patch cycle.
- Enforce Protected View for documents originating from the internet, email attachments, and unsafe locations.
- Restrict macros and active content in Office through Group Policy until patches are deployed.
Patch Information
Microsoft has published guidance in the Microsoft CVE-2026-64917 Advisory. Administrators should deploy the corresponding Office security update through Microsoft Update, WSUS, Microsoft Intune, or Configuration Manager. Verify the update installs on all Office channels in use, including Current, Monthly Enterprise, and Semi-Annual Enterprise.
Workarounds
- Block or quarantine inbound Word documents from external senders at the email gateway until patching completes.
- Configure Office File Block policy to prevent opening legacy or untrusted Word file formats.
- Train users to preview documents in Protected View and avoid enabling editing on unverified files.
# Example: enforce Protected View via Group Policy registry keys
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
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
