CVE-2026-20949: Microsoft Excel Security Feature Bypass Vulnerability

Overview

Severity

High (CVSS 7.8)

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Category

Security Feature Bypass

Exploit Status

Not Exploited

Exploitation Likelihood

Less Likely

Patch Tuesday

2026-Jan

Released

2026-01-13

EPSS Score

0.02% (percentile: 5.2%)

Description

Improper access control in Microsoft Office Excel allows an unauthorized attacker to bypass a security feature locally.

FAQ

What kind of security feature could be bypassed by successfully exploiting this vulnerability? The security feature bypassed is the macro security controls, specifically the setting that disables XL4 macros (Excel 4.0 macros). According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do? The user must open the malicious workbook, enable editing, and then click the attacker‑supplied Quick Access Toolbar (QAT) button, which triggers the XL4 macro despite Trust Center protections. Is the Preview Pane an attack vector for this vulnerability? No, the Preview Pane is not an attack vector.

Affected Products (8)

Microsoft Office

• Microsoft 365 Apps for Enterprise for 32-bit Systems
• Microsoft 365 Apps for Enterprise for 64-bit Systems
• Microsoft Office LTSC for Mac 2021
• Microsoft Office LTSC 2021 for 64-bit editions
• Microsoft Office LTSC 2021 for 32-bit editions
• Microsoft Office LTSC 2024 for 32-bit editions
• Microsoft Office LTSC 2024 for 64-bit editions
• Microsoft Office LTSC for Mac 2024

Security Updates (1)

• Release Notes

Acknowledgments

Anonymous

Revision History

• 2026-01-13: Information published.