CVE-2026-40420 | Microsoft Office Click-To-Run Elevation of Privilege Vulnerability

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

Published: 2026-05-12 Last update: 2026-06-01 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40420 is rated Low Risk (39.5/100): CVSS High severity, with low exploitation likelihood (EPSS 0.04%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-40420

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-13 — 0.04% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40420

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.0 6.0 [email protected]

Weakness enumeration for CVE-2026-40420

GitHub Security Advisory for CVE-2026-40420

GHSA-q3w4-cjqg-q4x3 · Severity: high — Improper access control in Microsoft Office Click-To-Run allows an authorized attacker to elevate...

Affected software / configurations for CVE-2026-40420

Vendor Product Version Raw CPE
microsoft 365_apps — cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
microsoft 365_apps — cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
microsoft office 2019 cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
microsoft office 2019 cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
microsoft office_long_term_servicing_channel 2021 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x64:*
microsoft office_long_term_servicing_channel 2021 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*
microsoft office_long_term_servicing_channel 2024 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*
microsoft office_long_term_servicing_channel 2024 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*

References for CVE-2026-40420

cvelogic Threat Intelligence