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vulnerability

CVE-2024-21413

9.8
Critical
KEV · Exploited in wildEPSS 95%Patch available

Microsoft Outlook Remote Code Execution Vulnerability

exploited
Yes, in CISA KEV since 6 Feb 2025fix by 27 Feb 2025 (CISA deadline for US federal agencies)unvetted proof-of-concept code on github
fix
Patch available see the advisory in the references
likelihood
EPSS 94.7%
Published 13 Feb 2024Analysed here 2 Nov 2026CVSS scored by the publisher (CNA)

do firstApply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

triage
surface unknownruntimeWAF can block: partlyAV · networkCWE-20· Improper Input Validation

Can a WAF block it? Partly. The bug can be reached over the network, so generic WAF rules may stop some attacks. Its weakness type is unknown, so we cannot be more precise.

Also consider: patch

Based on the weakness type only; no CVE-specific evidence yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.

cvss vector
attack vectornetworkattack complexitylowprivileges requirednoneuser interactionnonescopeunchangedconfidentialityhighintegrityhighavailabilityhigh
CVSS 3.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
common questions

Is CVE-2024-21413 being exploited?

Yes. CVE-2024-21413 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.

How severe is CVE-2024-21413?

CVE-2024-21413 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2024-21413?

Yes. A fix has been recorded for CVE-2024-21413. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2024-21413 affect?

CVE-2024-21413 affects microsoft:365_apps, microsoft:office_2016, microsoft:office_2019, microsoft:office_long_term_servicing_channel. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary
technical analysis
affected
microsoft:365_appsmicrosoft:office_2016microsoft:office_2019microsoft:office_long_term_servicing_channel
affected versions
Microsoft Microsoft 365 Apps for Enterprise
  • affected>= 16.0.1 and < https://aka.ms/OfficeSecurityReleases
Microsoft Microsoft Office 2016
  • affected>= 16.0.0 and < 16.0.5435.1001
Microsoft Microsoft Office 2019
  • affected>= 19.0.0 and < https://aka.ms/OfficeSecurityReleases
Microsoft Microsoft Office LTSC 2021
  • affected>= 16.0.1 and < https://aka.ms/OfficeSecurityReleases

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

public exploits

Unvetted proof-of-concept code on GitHub: 42 GitHub proofs of concept

Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.

cisa ssvc

exploitation
active
automatable
yes
technical impact
total

Assessed by CISA 7 Feb 2025 (SSVC 2.0.3).

timeline

  1. 13 Feb 2024Published
  2. 15 Feb 2024First proof-of-concept repository on GitHub (unvetted) · 1 day later
  3. 6 Feb 2025Added to CISA KEV (exploited in the wild) · 357 days (about 12 months) later
  4. 7 Feb 2025CISA SSVC assessment: exploitation active · 1 day later
  5. 27 Feb 2025CISA remediation due date (US federal agencies) · 20 days later
  6. 10 Aug 2026CVE record last updated · 530 days (about 1 year) later
  7. 2 Nov 2026Analysed by vulneraibility.com · 84 days (about 3 months) later
how to fix
Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.
references
NVDCVE.orgCVE DetailsSource
5 references in the CVE record: 1 patch, 4 links
  • Patchmsrc.microsoft.com /update-guide/vulnerability/CVE-2024-21413
  • Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-21413
  • Linkvicarius.io /vsociety/posts/cve-2024-21413-critical-monikerlink-vulnerability-affecting-micr
  • Linkvicarius.io /vsociety/posts/cve-2024-21413-critical-monikerlink-vulnerability-affecting-micr
  • Linkresearch.checkpoint.com /2024/the-risks-of-the-monikerlink-bug-in-microsoft-outlook-and-the-big-picture/

sources

  • CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
  • NVD: CVSS and CPE data
  • CISA KEV catalog: exploitation, date added, due date
  • CISA Vulnrichment (ADP): SSVC decision points
  • FIRST EPSS: exploit probability and percentile
  • PoC-in-GitHub: GitHub repositories that claim a proof of concept
  • Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
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