CVE-2021-26887: Microsoft Windows 10

High severity, CVSS 7.8. EPSS: 1.1% chance of exploitation in the next 30 days.

An elevation of privilege vulnerability exists in Microsoft Windows when Folder redirection has been enabled via Group Policy. When folder redirection file server is co-located with Terminal server, an attacker who successfully exploited the vulnerability would be able to begin redirecting another user's personal data to a created folder. To exploit the vulnerability, an attacker can create a new folder under the Folder Redirection root path and create a junction on a newly created User folder. When the new user logs in, Folder Redirection would start redirecting to the folder and copying personal data. This elevation of privilege vulnerability can only be addressed by reconfiguring Folder Redirection with Offline files and restricting permissions, and NOT via a security update for affected Windows Servers. See the FAQ section of this CVE for configuration guidance.

Affected products

• Microsoft Windows 10: affected versions not specified; version 20h2 only; version 1607 only; version 1803 only; version 1809 only; version 1909 only; …
• Microsoft Windows 7: affected versions not specified
• Microsoft Windows 8.1: affected versions not specified
• Microsoft Windows Rt 8.1: affected versions not specified
• Microsoft Windows Server 2008: affected versions not specified; version r2 only
• Microsoft Windows Server 2012: affected versions not specified; version r2 only
• Microsoft Windows Server 2016: affected versions not specified; version 20h2 only; version 1909 only; version 2004 only
• Microsoft Windows Server 2019: affected versions not specified

Published 2021-03-11. Last modified 2026-08-19.