CVE-2024-21413 Microsoft Outlook Improper Input Validation Vulnerability
Microsoft Outlook contains an improper input validation vulnerability that allows for remote code execution. Successful exploitation of this vulnerability would allow an attacker to bypass the Office Protected View and open in editing mode rather than protected mode.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 6 Feb 2025.
- Rated Critical severity (CVSS 9.8, scored by Vendor).
- It has been in the catalogue for 638 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Microsoft Outlook Remote Code Execution Vulnerability
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Microsoft 365 Apps for Enterprise | 16.0.1 to before https://aka.ms/OfficeSecurityReleases |
| Microsoft Microsoft Office 2016 | 16.0.0 to before 16.0.5435.1001 |
| Microsoft Microsoft Office 2019 | 19.0.0 to before https://aka.ms/OfficeSecurityReleases |
| Microsoft Microsoft Office LTSC 2021 | 16.0.1 to before https://aka.ms/OfficeSecurityReleases |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Microsoft Office Outlook. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
Fix it
Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
Vulnerability Management - 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
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