How severe is CVE-2026-40421?

CVE-2026-40421 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-40421 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40421?

CVE-2026-40421 primarily affects Microsoft 365 Apps. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-40421?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40421 have an EU (EUVD) identifier?

Yes. CVE-2026-40421 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29678.

When was CVE-2026-40421 published?

CVE-2026-40421 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-40421

CVE-2026-40421 is a medium-severity vulnerability in Microsoft 365 Apps with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-73.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
EPSS exploit prediction: 1% (45th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29678
Weakness: CWE-73
Affected product: Microsoft 365 Apps
Published: 2026-05-12
Last modified: 2026-06-17

Description

Files or directories accessible to external parties in Microsoft Office Word allows an unauthorized attacker to disclose information locally.

Frequently asked questions

What is CVE-2026-40421?: Files or directories accessible to external parties in Microsoft Office Word allows an unauthorized attacker to disclose information locally.
How severe is CVE-2026-40421?: CVE-2026-40421 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-40421 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40421?: CVE-2026-40421 primarily affects Microsoft 365 Apps. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-40421?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40421 have an EU (EUVD) identifier?: Yes. CVE-2026-40421 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29678.
When was CVE-2026-40421 published?: CVE-2026-40421 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40421

Affected products (10)

cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office:2024:*:*:*:ltsc:*:x64:*
cpe:2.3:a:microsoft:office:2024:*:*:*:ltsc:*:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:word:2016:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:word:2016:*:*:*:*:*:x86:*

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