How severe is CVE-2026-40420?

CVE-2026-40420 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-40420 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40420?

CVE-2026-40420 primarily affects Microsoft 365 Apps. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-40420?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-40420 have an EU (EUVD) identifier?

Yes. CVE-2026-40420 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29677.

When was CVE-2026-40420 published?

CVE-2026-40420 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-40420

CVE-2026-40420 is a high-severity vulnerability in Microsoft 365 Apps with a CVSS 3.x base score of 8.8. 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-284.

Key facts

Severity: High (CVSS 3.x base score 8.8)
EPSS exploit prediction: 0% (11th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29677
Weakness: CWE-284
Affected product: Microsoft 365 Apps
Published: 2026-05-12
Last modified: 2026-06-17

Description

Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.

Frequently asked questions

What is CVE-2026-40420?: Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.
How severe is CVE-2026-40420?: CVE-2026-40420 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-40420 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40420?: CVE-2026-40420 primarily affects Microsoft 365 Apps. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-40420?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-40420 have an EU (EUVD) identifier?: Yes. CVE-2026-40420 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29677.
When was CVE-2026-40420 published?: CVE-2026-40420 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40420

Affected products (8)

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_long_term_servicing_channel:2021:*:*:*:*:-:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*

More vulnerabilities in Microsoft 365 Apps

CVE-2024-21413 — Critical (CVSS 9.8): Microsoft Outlook Remote Code Execution Vulnerability
CVE-2023-23397 — Critical (CVSS 9.8): Microsoft Outlook Elevation of Privilege Vulnerability
CVE-2020-0901 — Critical (CVSS 9.8): A remote code execution vulnerability exists in Microsoft Excel software when the software fails to properly handle…
CVE-2023-33150 — Critical (CVSS 9.6): Microsoft Office Security Feature Bypass Vulnerability
CVE-2026-35436 — High (CVSS 8.8): Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.
CVE-2024-38189 — High (CVSS 8.8): Microsoft Project Remote Code Execution Vulnerability

All CVEs affecting Microsoft 365 Apps →

Other CWE-284 (Improper Access Control) vulnerabilities

CVE-2026-50746 — Critical (CVSS 10.0): A malicious actor with access to the network could exploit an Improper Access Control vulnerability found in UniFi…
CVE-2026-46978 — Critical (CVSS 10.0): Vulnerability in the Oracle Solaris product of Oracle Systems (component: Remote Administration Daemon). The…
CVE-2026-35308 — Critical (CVSS 10.0): Vulnerability in the Oracle Coherence product of Oracle Fusion Middleware (component: Centralized Third Party Jars).…
CVE-2026-35307 — Critical (CVSS 10.0): Vulnerability in the Oracle Coherence product of Oracle Fusion Middleware (component: Core). Supported versions that…
CVE-2026-46695 — Critical (CVSS 10.0): Boxlite is a sandbox service that allows users to create lightweight virtual machines (Boxes) and launch OCI containers…
CVE-2026-46840 — Critical (CVSS 10.0): Vulnerability in Oracle REST Data Services (component: Backend-as-a-Service). Supported versions that are affected are…

Browse all CWE-284 (Improper Access Control) vulnerabilities →