Outlook prompts security notice opening .ICS files after installing protections for Microsoft Outlook Information Disclosure Vulnerability released: Dec 12, 2023

Last Updated: August 30, 2024

ISSUE

When you click to open an .ICS file you are prompted with the following warning: 

“Microsoft Office has identified a potential security concern.

This location may be unsafe.”

This issue happens after installing the Outlook Desktop December 12th security updates. For additional information see the respective CVEs. CVE-2023-35636 - Security Update Guide - Microsoft - Microsoft Outlook Information Disclosure Vulnerability

STATUS: FIXED

A secondary fix for the security prompt showing when opening an ICS attachment from an email is fixed in the following channels:
Beta Channel:  Version 2409 (Build 18027.15000)
Current Channel:  Version 2410 (Build 18129.20000) ETA late October 2024

Opening an ICS from a local file path is fixed in the July 9th, 2024 public updates for Outlook Desktop. The fixed builds are listed below:

2407 17830.20000
2406 17726.20148
2405 17628.20182
2404 17531.20206
2402 17328.20452
2308 16731.20732
5456.1000

If you set the registry keys below to temporarily disable the security notice, you can test removing them and confirm the latest fix addresses the issue.

If you decide to use the registry key, please be aware it will stop security notice prompts for all types of files and not just for the .ICS files.

If you need to disable this dialog, follow the instructions in the article Enable or disable hyperlink warning messages in Office programs.

Group Policy registry path:

HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\common\security
DWORD: DisableHyperlinkWarning
Value: 1

OCT registry path:

Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Security
DWORD: DisableHyperlinkWarning
Value: 1