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Privacy Statement Third-Party Cookies Accept Reject Manage cookies MSRC  Customer Guidance  Security Update Guide  Vulnerabilities  CVE-2026-40420 Microsoft Office Click-To-Run Elevation of Privilege Vulnerability New On this page  CVE-2026-40420  Subscribe RSS PowerShell  API  CSAF Security Vulnerability Released: May 12, 2026 Assigning CNA Microsoft CVE.org link CVE-2026-40420  Impact Elevation of Privilege Max Severity Important Weakness CWE-284: Improper Access Control CVSS Source Microsoft Vector String CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C Metrics CVSS:3.1 8.8 / 7.7  Base score metrics: 8.8 / Temporal score metrics: 7.7  Expand all  Collapse all Metric Value   Base score metrics(8) Attack Vector Local Attack Complexity Low Privileges Required Low User Interaction None Scope Changed Confidentiality High Integrity High Availability High   Temporal score metrics(3) Exploit Code Maturity Unproven Remediation Level Official Fix Report Confidence Confirmed Please see Common Vulnerability Scoring System for more information on the definition of these metrics. Executive Summary Improper access control in Microsoft Office Click-To-Run allows an authorized attacker to elevate privileges locally. Exploitability The following table provides an exploitability assessment for this vulnerability at the time of original publication. Publicly disclosed No Exploited No Exploitability assessment Exploitation Less Likely FAQ Is the Preview Pane an attack vector for this vulnerability? No, the Preview Pane is not an attack vector. According to the CVSS metric, a successful exploitation could lead to a scope change (S:C). What does this mean for this vulnerability? This vulnerability could lead to a browser sandbox escape. What privileges could be gained by an attacker who successfully exploited this vulnerability? An attacker who successfully exploited this vulnerability could gain SYSTEM privileges. Acknowledgements Ben Lichtman with Microsoft Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgements for more information. Security Updates To determine the support lifecycle for your software, see the Microsoft Support Lifecycle. Release date Descending  Edit columns  Download  Filters  Product Family  Max Severity  Impact  Platform   Clear Release date  Product Platform Impact Max Severity Article Download Build Number Assigning CNA Customer Action Required Title: Release date, Content: May 12, 2026 Microsoft Office LTSC 2024 for 64-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office LTSC 2024 for 64-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office LTSC 2024 for 64-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft Office LTSC 2024 for 32-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office LTSC 2024 for 32-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office LTSC 2024 for 32-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft Office LTSC 2021 for 32-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office LTSC 2021 for 32-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office LTSC 2021 for 32-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft Office LTSC 2021 for 64-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office LTSC 2021 for 64-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office LTSC 2021 for 64-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft 365 Apps for Enterprise for 64-bit Systems - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft 365 Apps for Enterprise for 64-bit Systems, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft 365 Apps for Enterprise for 64-bit Systems, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft 365 Apps for Enterprise for 32-bit Systems - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft 365 Apps for Enterprise for 32-bit Systems, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft 365 Apps for Enterprise for 32-bit Systems, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft Office 2019 for 64-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office 2019 for 64-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office 2019 for 64-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required Title: Release date, Content: May 12, 2026 Microsoft Office 2019 for 32-bit editions - Elevation of Privilege Important Title: Knowledge Base Articles for Microsoft Office 2019 for 32-bit editions, Content:, 1 link Click to Run  Title: Download Security Update for Microsoft Office 2019 for 32-bit editions, Content:, 1 link Security Update Title: Build numbers, Content: https://aka.ms/OfficeSecurityReleases Title: Assigning CNA, Content: Microsoft Title: Customer action required, Content: Required All results loaded Loaded all 8 rows Disclaimer The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. Revisions version revisionDate description 1.0 May 12, 2026 Information published.  How satisfied are you with the MSRC Security Update Guide? Rating  Broken  Bad  Below average  Average  Great!  Your Privacy Choices Consumer Health Privacy