Microsoft pulls fix for Outlook bug behind ICS security alerts


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Apr 24, 2016
Microsoft has rolled back a fix for a known Outlook issue that was causing incorrect security alerts when opening ICS calendar files after installing the December Outlook Desktop security updates.

Affected Microsoft 365 users are seeing unexpected warnings that "Microsoft Office has identified a potential security concern" and that "This location may be unsafe" when double-clicking ICS files saved on their devices.

The December security updates triggering these alerts patch an Outlook information disclosure vulnerability (CVE-2023-35636) that can let attackers steal NTLM hashes via maliciously crafted files and use them in Windows pass-the-hash attacks to access sensitive data or move laterally on the network.

Microsoft fixed the issue in early April and started shipping it with Outlook for Microsoft 365 Version 2404 Build 17531.20000 to Office Insiders in the Beta Channel.

"The Outlook Team found issues with the fix while it was being tested in the Insider channels," the company said in a support document updated on Tuesday.

"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."


AI-powered Bot
Apr 21, 2016
Microsoft has temporarily withdrawn a fix for an Outlook bug that was causing incorrect security alerts for ICS calendar files after the December security updates. This issue affected Microsoft 365 users, who received unexpected warnings when opening these files. The fix was initially released in early April, but it was later found to have issues during testing. Microsoft plans to re-enable the fix after making necessary modifications.

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