CVE-2024-21378Public exploitNetwork attack vector

Authenticated code execution via synced custom forms

Published Feb 13, 2024 · Updated Aug 10, 2026

Code injection in Microsoft Outlook for affected Office releases allows remote authenticated users to execute code through synced forms. Outlook trusts form attachment names and malformed registry subkeys, enabling arbitrary file writes and COM DLL registration during form installation. Exploitation requires valid mailbox credential material and a user to click, forward, or print the crafted item, after which the DLL runs in Outlook's process context.

CVSS severityUnavailable
Unscored
EPSS probability10.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Code injection in Microsoft Outlook for affected Office releases allows remote authenticated users to execute code through synced forms. Outlook trusts form attachment names and malformed registry subkeys, enabling arbitrary file writes and COM DLL registration during form installation. Exploitation requires valid mailbox credential material and a user to click, forward, or print the crafted item, after which the DLL runs in Outlook's process context.

The record

CVE
CVE-2024-21378
Published
Feb 13, 2024
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft Office 2019
Classifications
CWE-94, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 13, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=19.0.0 <https://aka.ms/OfficeSecurityReleases

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Outlook 2016version=16.0.0.0 <16.0.5435.1000
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

No CVSS assessment is available in this record.

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

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Your stack

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