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

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 6 Feb 2025, 359 days after the CVE record was published.

How likely is exploitation in the next 30 days?

94.7%

EPSS score, percentile 99.9 of all scored records

How severe?

9.8 Critical

CVSS v3.1 base score, given by the CNA

What should I do?

CISA deadline 27 Feb 2025. Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected

• 16.0.1
• from 16.0.0 to before 16.0.5435.1001
• 19.0.0
• 16.0.1

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 27 February 2025.

Advisories and patches

• Microsoft Outlook Remote Code Execution Vulnerability (Vendor advisory, Patch)

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-21413
• https://nvd.nist.gov/vuln/detail/CVE-2024-21413

Affected products and versions

As listed in the CVE record.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this 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.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2024-21413 to its Known Exploited Vulnerabilities (KEV) catalog on 6 Feb 2025.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 27 Feb 2025.
• The CVE record was published on 13 Feb 2024, 359 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 94.7% (percentile 99.9), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Microsoft Outlook Remote Code Execution Vulnerability

Microsoft Outlook Remote Code Execution Vulnerability

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-20: Improper Input Validation

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

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