CVE-2024-43609 Overview
CVE-2024-43609 is a spoofing vulnerability affecting Microsoft Office and Microsoft 365 Apps. Microsoft published the advisory on October 8, 2024, as part of its monthly security update cycle. The flaw is categorized under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor) and requires user interaction over a network vector. Successful exploitation allows an attacker to spoof content or expose sensitive information such as NTLM hashes to an untrusted party.
Critical Impact
An attacker can trick a user into opening a crafted Office file, leading to spoofed content presentation or leakage of authentication material that supports follow-on relay or offline cracking attacks.
Affected Products
- Microsoft 365 Apps (Enterprise)
- Microsoft Office 2016 (x86 and x64)
- Microsoft Office 2019 and Microsoft Office LTSC 2021/2024
Discovery Timeline
- 2024-10-08 - Microsoft releases security patch and publishes advisory
- 2024-10-08 - CVE-2024-43609 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-43609
Vulnerability Analysis
CVE-2024-43609 is a spoofing vulnerability in Microsoft Office client applications. The weakness is mapped to [CWE-200], indicating unauthorized exposure of sensitive information. Exploitation requires an attacker to convince a user to open or interact with a malicious Office document delivered through email, a web link, or file share. Once the file is opened, Office initiates a request that can leak protected information to an attacker-controlled endpoint or misrepresent content within the application interface.
The primary impact is against integrity. Confidentiality and availability are not directly affected by the flaw itself, but disclosed authentication material can enable secondary attacks. Attackers commonly leverage such spoofing issues to trigger outbound authentication from the victim host, capturing NTLM challenge/response pairs for relay against internal services.
Root Cause
The root cause is improper handling of embedded references or protocol handlers within Office documents. Office resolves the reference without adequate validation of the target origin, allowing an attacker-supplied path to appear trusted to the user or to trigger implicit authentication. Microsoft has not published low-level technical details in the public advisory.
Attack Vector
The attack requires user interaction. A remote attacker delivers a crafted Office document to the victim and induces them to open it. Upon rendering, the document causes Office to load or reference attacker-controlled content, either presenting misleading UI elements or emitting an authenticated network request. Refer to the Microsoft Security Update Guide for CVE-2024-43609 for vendor guidance.
No public proof-of-concept or exploit code has been observed for this vulnerability at the time of writing.
Detection Methods for CVE-2024-43609
Indicators of Compromise
- Outbound SMB (TCP/445) or WebDAV traffic from winword.exe, excel.exe, or powerpnt.exe to untrusted external hosts.
- Office documents containing embedded UNC paths, remote template references, or unusual protocol handlers such as file:// or \\attacker\share.
- Anomalous NTLM authentication attempts originating from workstations shortly after users open email attachments.
Detection Strategies
- Inspect Office documents at the mail gateway for embedded external references and remote template links prior to delivery.
- Correlate process telemetry from Office applications with outbound network connections to non-corporate destinations.
- Alert on Office child processes or authentication events that follow the opening of documents from external senders.
Monitoring Recommendations
- Enable Microsoft Office telemetry and Attack Surface Reduction (ASR) audit logs to track document behavior.
- Monitor egress firewall logs for SMB, WebDAV, and LDAP traffic from user endpoints to the internet.
- Track Windows Security event ID 4624 and 4648 patterns tied to Office process lineage for signs of forced authentication.
How to Mitigate CVE-2024-43609
Immediate Actions Required
- Apply the October 2024 Microsoft security updates for all affected Office and Microsoft 365 Apps builds without delay.
- Block outbound SMB (TCP/445) and unauthenticated WebDAV traffic from user workstations to the public internet at the perimeter.
- Enforce SMB signing and disable NTLM where feasible to reduce the value of any leaked authentication material.
Patch Information
Microsoft released fixes for CVE-2024-43609 on October 8, 2024, covering Microsoft 365 Apps for Enterprise, Office 2016, Office 2019, and Office LTSC 2021 and 2024. Deploy the updates listed in the Microsoft Security Update Guide for CVE-2024-43609 through your standard patch management process. Validate that all channel builds (Current, Monthly Enterprise, Semi-Annual) receive the corresponding update.
Workarounds
- Configure the RestrictSendingNTLMTraffic Group Policy to block NTLM authentication to remote servers.
- Disable automatic loading of remote content and linked objects in Office via Trust Center policies.
- Deliver Office documents from external senders through Protected View and disable editing by default.
# Group Policy registry settings to restrict outbound NTLM and enforce Protected View
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" /v RestrictSendingNTLMTraffic /t REG_DWORD /d 2 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableAttachmentsInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /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.
