CVE-2024-21413: Fixing the MonikerLink vulnerability in Outlook

MonikerLink - the zero-day CVE-2024-21413 - has been discovered in Microsoft Outlook and requires attention. Here's what you need to know.

VE-2024-21413, a critical zero-day vulnerability dubbed the MonikerLink bug, has been discovered in Microsoft Outlook. This post aims to provide a comprehensive understanding of the vulnerability, its potential impact, and actionable steps for mitigation.

Here’s everything you need to know about CVE-2024-21413:

What you’ll learn

  1. What is CVE-2024-21413?
  2. Does CVE-2024-21413 affect me?
  3. Has CVE-2024-21413 been actively exploited in the wild?
  4. How to fix CVE-2024-21413
  5. Next steps 

What is CVE-2024-21413?

CVE-2024-21413, also known as the MonikerLink bug, is a zero-day vulnerability identified in Microsoft Outlook, a widely-used email client. This vulnerability allows attackers to execute arbitrary code remotely on a victim’s machine by exploiting specific types of hyperlinks within Outlook. By manipulating the URL of a hyperlink in a malicious manner, attackers can bypass Outlook’s security mechanisms and gain unauthorized access to sensitive information or take control of the victim’s system.

Does CVE-2024-21413 affect me?

CVE-2024-21413 poses a significant risk to users of Microsoft Outlook across various versions and platforms. Any individual or organization using Outlook for email communication is potentially vulnerable to exploitation through this zero-day vulnerability. It’s crucial for users to be aware of this threat and take immediate steps to protect themselves against potential attacks.


Has CVE-2024-21413 been actively exploited in the wild?

As of the time of writing, CVE-2024-21413 is classified as a zero-day vulnerability, indicating that it has been actively exploited by malicious actors in the wild before the vendor became aware of it. Attackers may have already leveraged this vulnerability to launch targeted attacks against unsuspecting users. Given the severity of the risk, users must remain vigilant and take immediate action to mitigate the threat.

How to fix CVE-2024-21413

Microsoft has released a critical security update for Outlook to address CVE-2024-21413 and mitigate the associated risks as part of their February 2024 Patch Tuesday updates. Users are strongly urged to apply this patch immediately to protect their systems from potential exploitation. Additionally, users can enhance their security posture by:
  • Exercising caution when clicking on hyperlinks, especially in unsolicited or suspicious emails.
  • Employing robust email security solutions capable of detecting and blocking malicious content.
  • Educating users about cybersecurity best practices and raising awareness of the zero-day vulnerability.

Next steps 

Each new vulnerability is a reminder of where we stand and what we need to do better. Check out the following resources to help you maintain cyber hygiene and stay ahead of the threat actors: 

  1. 2023 Vulnerability watch reports 
  2. MITRE ATTACK framework – Mapping techniques to CVEs  
  3. The true impact of exploitable vulnerabilities for 2024
  4. Multi-cloud security challenges – a best practice guide
  5. How to properly tackle zero-day threats

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