---
title: "CVE-2024-21413: Microsoft Outlook Improper Input Validation Vulnerability"
url: https://erroneo.us/security/cve/CVE-2024-21413/
description: "CVE-2024-21413 (Microsoft Office Outlook): Exploited in the wild (CISA KEV). Microsoft Outlook Remote Code Execution Vulnerability"
type: vulnerability-record
section: "Security Digest"
date_published: 2024-02-13
date_modified: 2026-08-10
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2024-21413"
kev: true
cvss: 9.8
epss: 0.9466
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2024-21413: Microsoft Outlook Improper Input Validation Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft Office Outlook. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-02-06, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-02-27 ; treat that as the outer limit, not the target.
- EPSS 94.7% , percentile 99.9: FIRST’s model estimates a 94.7% chance of exploitation activity in the next 30 days, higher than 99.9% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

## What it is

Microsoft Outlook Remote Code Execution Vulnerability

## Affected products (CVE record)

- Microsoft Microsoft 365 Apps for Enterprise: 16.0.1 < https://aka.ms/OfficeSecurityReleases
- Microsoft Microsoft Office 2016: 16.0.0 < 16.0.5435.1001
- Microsoft Microsoft Office 2019: 19.0.0 < https://aka.ms/OfficeSecurityReleases
- Microsoft Microsoft Office LTSC 2021: 16.0.1 < https://aka.ms/OfficeSecurityReleases

## Severity

- microsoft CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`

## Exploitation

- CISA KEV: added 2025-02-06; federal due date 2025-02-27. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 94.66% probability of exploitation activity in the next 30 days; percentile 99.9.

## Sources

- [Microsoft Outlook Remote Code Execution Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-21413)
- [CVE.org record CVE-2024-21413](https://www.cve.org/CVERecord?id=CVE-2024-21413)
- [NVD entry CVE-2024-21413](https://nvd.nist.gov/vuln/detail/CVE-2024-21413)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-21413)
- [vicarius.io](https://www.vicarius.io/vsociety/posts/cve-2024-21413-critical-monikerlink-vulnerability-affecting-microsoft-outlook-mitigation-script)
- [vicarius.io](https://www.vicarius.io/vsociety/posts/cve-2024-21413-critical-monikerlink-vulnerability-affecting-microsoft-outlook-detection-script)
- [research.checkpoint.com](https://research.checkpoint.com/2024/the-risks-of-the-monikerlink-bug-in-microsoft-outlook-and-the-big-picture/)

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Source page: https://erroneo.us/security/cve/CVE-2024-21413/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt