Outlook has identified a security flaw that affects how it handles certain hyperlinks. 

Malware actors actively exploit the vulnerability in real-world attacks.

The assigned CVE number for this vulnerability is CVE-2024-21413, with a severity rating of 9.8 (Critical).

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Microsoft has successfully resolved the vulnerability in question and implemented the fix in their February 2024 Patch Tuesday release.

In case of successful exploitation of the vulnerability, a malicious actor can bypass the protected view of Office and open a file in editing mode instead of the protected mode.

Outlook 0-Day RCE Flaw

According to the Checkpoint report, if the hyperlink starts with http:// or https://, Outlook uses Windows’s default browser to open the URL.

If there are additional protocols, such as the “Skype” URL protocol, clicking on the hyperlink will trigger a security warning.

In other cases, like the “file://” protocol, Outlook did not display a warning dialog box.

A slight modification in the “file://” protocol link bypasses the previously shown security restriction and proceeds to access the resource.

According to experts, utilizing this particular resource involves utilizing the SMB protocol.

However, this protocol has a flaw where it inadvertently reveals the local NTLM credentials during the access process.

Exploit on Hacking Forums

The Daily Dark Web recently reported that specific hacking forums have been discussing an exploit for CVE-2024-21413.

This exploit allows attackers to access NTLM information and execute remote code.

The vulnerability can exploit the Office Protected View and use it as a means of attack to target other Office applications.

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