Critical Microsoft Outlook RCE Vulnerability (CVE-2024-21413): What Organisations Must Know

Critical Microsoft Outlook RCE Vulnerability (CVE-2024-21413): What Organisations Must Know

A newly discovered and actively exploited vulnerability in Microsoft Outlook has sent shockwaves across the global cybersecurity community. Identified as CVE-2024-21413, this flaw allows attackers to execute malicious code on a victim’s system simply by sending a specially crafted email. The most alarming part is that the victim may not even need to click on anything for the attack to succeed.

At Terra System Labs, we consider this vulnerability extremely serious due to its ease of exploitation and the massive number of users relying on Microsoft Outlook every day.

What is CVE-2024-21413?

CVE-2024-21413 is a remote code execution vulnerability that affects how Microsoft Outlook processes certain types of links. The issue exists in the way Outlook handles specially crafted file-based URLs. When a user receives a malicious email containing such a payload, simply previewing the message can trigger the exploit.

This means an attacker can remotely execute code on the victim’s machine without:

• Any file attachment

• Any visible warning

• Any user interaction beyond opening or previewing the email

Once exploited, attackers can take full control of the affected system. This includes installing malware, stealing sensitive information, creating backdoors, or moving laterally inside an organisation’s network.

Is the Exploit Being Used in Real Attacks?

Yes. What makes this case especially dangerous is that:

• The exploit is already being used in real-world attacks

• Public proof-of-concept code is available on GitHub

• Threat actors can easily weaponise it

Once an exploit becomes public, the chances of mass exploitation increase rapidly. This puts unpatched organisations at extremely high risk.

The exploit code is available on GitHub cab be found here.

Who is Affected?

This vulnerability impacts a wide range of Microsoft products, including:

• Microsoft Outlook with Office 2016

• Microsoft Outlook with Office 2019

• Microsoft Office LTSC 2021

• Microsoft 365 Apps for Enterprise

Both 32-bit and 64-bit versions are affected. Since Outlook is widely used across enterprises, government bodies, BFSI organisations, and remote work environments, the potential attack surface is massive.

Why This Vulnerability Is Extremely Dangerous

Several factors make this vulnerability highly critical:

• Zero-click style attack where previewing the email is enough

• No attachment is required, making detection harder

• Can lead to full system compromise

• Can expose internal credentials and authentication tokens

• Enables lateral movement within the corporate network

• High likelihood of being used in phishing and targeted attacks

This turns a simple email into a powerful cyber weapon.

What Has Microsoft Done?

Microsoft released official security updates in February 2024 to fix this vulnerability. Systems that have installed the latest Office and Outlook updates are protected against CVE-2024-21413. However, any system that remains unpatched is still exposed and vulnerable.

What Should Organisations Do Immediately?

At Terra System Labs, we strongly recommend the following immediate actions:

1. Apply Patches Without Delay

Ensure that all Outlook and Microsoft Office installations are updated across all employee systems, including remote devices.

2. Strengthen Email Security Controls

Update email security gateways to block suspicious URL schemes and abnormal link behaviors.

3. Monitor Endpoint Activity

Watch for unusual behavior such as Outlook launching unknown processes or strange outbound connections.

4. Improve User Awareness

Educate employees that email previews and links can be dangerous even without attachments.

5. Conduct a Security Assessment

A professional vulnerability assessment can help identify whether your organisation is already exposed or compromised.

Why This Matters for Businesses

This incident clearly highlights one critical truth: email remains the most powerful attack vector in today’s threat landscape. Even trusted software like Microsoft Outlook can become a gateway for attackers.

For businesses, this vulnerability can lead to:

• Data breaches

• Ransomware infections

• Credential theft

• Compliance violations

• Major financial and reputational damage

Proactive security is no longer optional. It is a necessity.

How Terra System Labs Can Help

At Terra System Labs, we help organisations stay ahead of threats through:

• Vulnerability Assessment and Penetration Testing

• Red Team and Attack Simulation

• Email Security Hardening

• Endpoint Detection and Response Validation

• Cybersecurity Awareness Training

• Compliance and Risk Advisory

If your organisation uses Outlook, we highly recommend a rapid security review to ensure this vulnerability is fully mitigated.

Final Thoughts

CVE-2024-21413 is a serious wake-up call for organisations that rely heavily on email communication. A single unpatched system can become the weak link that compromises an entire network.

Patch immediately. Review your security controls. Educate your teams. And most importantly, adopt a proactive cybersecurity strategy before attackers take advantage.

If you need expert support, Terra System Labs is here to help secure your digital ecosystem.