CVE-2024-21413Known exploitationPublic exploitNetwork attack vector

Remote code execution via unsafe Moniker parsing

Published Feb 13, 2024 · Updated Aug 10, 2026

Improper input validation in Microsoft Outlook in affected Office releases allows remote attackers to execute code through a crafted email. Outlook passes a crafted file-scheme Moniker Link to MkParseDisplayName, which resolves attacker-controlled remote content outside Protected View. Microsoft scores the flaw as requiring no user interaction, while the published Moniker Link demonstration requires the recipient to activate the link; exploitation can disclose NTLM credentials or run code in the user's context.

CVSS severity9.8
Critical
EPSS probability94.66%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Microsoft Outlook in affected Office releases allows remote attackers to execute code through a crafted email. Outlook passes a crafted file-scheme Moniker Link to MkParseDisplayName, which resolves attacker-controlled remote content outside Protected View. Microsoft scores the flaw as requiring no user interaction, while the published Moniker Link demonstration requires the recipient to activate the link; exploitation can disclose NTLM credentials or run code in the user's context.

The record

CVE
CVE-2024-21413
Published
Feb 13, 2024
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft Office 2016
Classifications
CWE-20, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 13, 2024CVE publishedPublication date reported by the CVE source.
  2. Feb 6, 2025Exploitation reportedCISA Known Exploited Vulnerabilities catalog entry
  3. Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.0.0 <16.0.5435.1001

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office 2016version=16.0.0 <16.0.5435.1001
Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Office LTSC 2021version=16.0.1 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft 365 Apps for enterpriseversion=16.0.1 <https://aka.ms/OfficeSecurityReleases

Published CVSS scores

9.8Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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