CVE-2026-45466: Microsoft Word Buffer Overflow Flaw

CVE-2026-45466 Overview

CVE-2026-45466 is a heap-based buffer overflow [CWE-122] in Microsoft Office Word. The vulnerability allows an unauthorized local attacker to disclose information when a user opens a crafted document. Exploitation requires user interaction but no prior authentication. The flaw affects the confidentiality of data accessible to the Word process and does not impact integrity or availability.

Microsoft published the security update guidance for this issue, and the CVE entry was added to the National Vulnerability Database (NVD) shortly after.

Critical Impact
Successful exploitation leaks heap memory contents from the Microsoft Word process, potentially exposing sensitive document data or in-memory secrets to an attacker-controlled document.

Affected Products

Microsoft Office Word (specific build numbers listed in the Microsoft Security Response Center advisory)

Discovery Timeline

2026-06-09 - CVE-2026-45466 published to NVD
2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-45466

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow within Microsoft Office Word's document parsing logic. When Word processes a malformed document structure, the code writes or reads beyond an allocated heap buffer. The resulting memory access leaks adjacent heap data back to the attacker through the parsed document's rendered content or telemetry surfaces.

The issue is classified under [CWE-122] Heap-based Buffer Overflow. The impact is constrained to information disclosure rather than code execution, which limits the blast radius but still exposes process memory that may contain document fragments, cached credentials, or session artifacts.

The Exploit Prediction Scoring System (EPSS) currently lists a low probability of exploitation activity in the near term, and no public proof-of-concept exploit has been published. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The root cause is improper bounds validation on a heap-allocated buffer during document object parsing. The parser trusts a length or offset value embedded in the document file without verifying it against the allocated buffer size. Microsoft has not published the exact field or parser routine in the public advisory.

Attack Vector

An attacker crafts a malicious Word document and delivers it to the victim through email, file share, or download. The victim must open the document in a vulnerable version of Word for exploitation to succeed. The attack is local and requires user interaction, which raises the practical barrier to mass exploitation. No network access to the target is required by the attacker.

No verified exploitation code is publicly available for this vulnerability. Refer to the Microsoft Security Update CVE-2026-45466 advisory for vendor-supplied technical context.

Detection Methods for CVE-2026-45466

Indicators of Compromise

Word documents (.doc, .docx, .rtf) received from untrusted senders that trigger unexpected Word process crashes or memory faults.
Anomalous child processes or memory dump activity originating from winword.exe after a document is opened.
Outbound network connections from winword.exe shortly after a document open event.

Detection Strategies

Monitor endpoint telemetry for crashes in winword.exe with heap corruption signatures such as Watson or Windows Error Reporting bucket IDs.
Inspect email gateways and content security tools for malformed Office documents flagged by structural validators.
Correlate document open events with subsequent unusual file or memory access patterns by the Office process.

Monitoring Recommendations

Enable audit logging for Office application crashes and forward to a central SIEM or data lake for correlation.
Track Microsoft Office build versions across the fleet and alert on hosts running unpatched builds listed in the MSRC advisory.
Apply attack surface reduction (ASR) rules in Microsoft Defender to block Office child process creation and suspicious behaviors.

How to Mitigate CVE-2026-45466

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-45466 advisory to all systems running Microsoft Office Word.
Prioritize patching on endpoints belonging to users who routinely open external documents, such as finance, HR, and executive staff.
Verify update deployment status through Microsoft Endpoint Manager, WSUS, or your existing patch management tooling.

Patch Information

Microsoft has released a security update through the Microsoft Security Response Center. Consult the Microsoft Security Update CVE-2026-45466 advisory for the exact KB numbers and affected build ranges. Apply updates through Windows Update, Microsoft Update, or the Microsoft 365 Apps update channel matching your deployment.

Workarounds

Open untrusted Word documents in Protected View, which sandboxes parsing and reduces exposure to memory disclosure.
Block or quarantine inbound .doc, .docx, and .rtf attachments from external senders at the email gateway until patches are applied.
Disable preview pane rendering of Office documents in Outlook and Windows Explorer to prevent inadvertent parsing.

bash

# Example: enforce Protected View for files from the internet via Group Policy registry key
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f