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

Last Updated: April 23, 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: WORKAROUND

The Outlook Team found issues with the fix while it was being tested in the Insider channels. Currently the fix has been disabled and will be re-enabled after some modifications. We will update this topic as soon as the fix is available again for testing.

In the meantime, if you need to temporarily disable the security notice you can use the registry key below. 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