CVE-2024-21413 Microsoft Outlook Improper Input Validation Vulnerability

CVE-2024-21413 is a critical security vulnerability identified in Microsoft Outlook, allowing attackers to execute arbitrary code remotely by exploiting improper input validation. This flaw enables the bypassing of Office’s Protected View, leading to potential unauthorized access and control over affected systems.

What is Vulnerable to CVE-2024-21413

The vulnerability affects multiple versions of Microsoft Office, including:

• Microsoft Office 2016
• Microsoft Office 2019
• Microsoft Office 2021
• Microsoft 365 Apps

Notably, the Outlook Web Application (OWA) is not impacted.

Mitigation and Remediation for CVE-2024-21413

To protect systems from this vulnerability, consider the following steps:

1. Apply Official Patches: Microsoft has released security updates to address this issue. Users should promptly update their Office installations via Windows Update.

   msrc.microsoft.com

2. Disable Automatic Link Previews: Configure Outlook to disable automatic link previews to prevent the automatic execution of malicious links.

3. Network-Level Protections: Implement firewall rules to block outbound SMB traffic, reducing the risk of NTLM hash leakage.

4. User Education: Train users to recognize and avoid suspicious emails and links, emphasizing the importance of not interacting with unexpected attachments or hyperlinks.

Impact of Successful Exploitation of CVE-2024-21413

Exploiting this vulnerability enables attackers to:

• Execute Arbitrary Code: Attackers can run malicious code with the same privileges as the Outlook application, potentially leading to full system compromise.

• Bypass Protected View: The flaw allows malicious documents to open directly in editing mode, circumventing the Protected View feature designed to safeguard users from untrusted files.

• Obtain NTLM Hashes: Attackers can capture NTLM hashes, which can be used in Pass-the-Hash attacks to impersonate users and gain unauthorized access to network resources.

The attack can be initiated through a crafted email containing a malicious link, requiring minimal user interaction.

Proof of Concept for CVE-2024-21413

A proof-of-concept (PoC) exploit for this vulnerability has been developed and is publicly available. The PoC demonstrates how an attacker can craft an email with a malicious link that, when processed by Outlook, leads to the execution of arbitrary code without user intervention.

Given the availability of this PoC and the critical nature of the vulnerability, it is imperative for organizations and individuals to apply the recommended mitigations promptly to protect their systems.