Microsoft Windows Folder Redirection Elevation of Privilege Vulnerability

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Summary

CVECVE-2021-26887
StatePUBLISHED
Assignermicrosoft
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-03-11 16:15:15 UTC
Updated2026-08-19 17:17:44 UTC
DescriptionAn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.009210000 probability, percentile 0.575180000 (date 2026-08-19)

Problem Types: CWE-59 | Elevation of Privilege

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1[email protected]Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNACVSS7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
2.0[email protected]Primary4.6AV:L/AC:L/Au:N/C:P/I:P/A:P

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v2.0 Breakdown

Access Vector
Local
Access Complexity
Low
Authentication
None
Confidentiality
Partial
Integrity
Partial
Availability
Partial

AV:L/AC:L/Au:N/C:P/I:P/A:P

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Microsoft Windows 10 - All All All
Operating System Microsoft Windows 10 1607 All All All
Operating System Microsoft Windows 10 1803 All All All
Operating System Microsoft Windows 10 1809 All All All
Operating System Microsoft Windows 10 1909 All All All
Operating System Microsoft Windows 10 2004 All All All
Operating System Microsoft Windows 10 20h2 All All All
Operating System Microsoft Windows 7 - sp1 All All
Operating System Microsoft Windows 8.1 - All All All
Operating System Microsoft Windows Rt 8.1 - All All All
Operating System Microsoft Windows Server 2008 - sp2 All All
Operating System Microsoft Windows Server 2008 r2 sp1 All All
Operating System Microsoft Windows Server 2012 - All All All
Operating System Microsoft Windows Server 2012 r2 All All All
Operating System Microsoft Windows Server 2016 - All All All
Operating System Microsoft Windows Server 2016 1909 All All All
Operating System Microsoft Windows Server 2016 2004 All All All
Operating System Microsoft Windows Server 2016 20h2 All All All
Operating System Microsoft Windows Server 2019 - All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Microsoft Windows 10 Version 1507 affected - 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1607 affected - 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1803 affected - 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1809 affected - 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1809 affected - ARM64-based Systems
CNA Microsoft Windows 10 Version 1909 affected - 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 10 Version 2004 affected - 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 10 Version 20H2 affected - 32-bit Systems, ARM64-based Systems
CNA Microsoft Windows 7 affected - 32-bit Systems
CNA Microsoft Windows 7 Service Pack 1 affected - x64-based Systems
CNA Microsoft Windows 8.1 affected - 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows Server 2008 R2 Service Pack 1 affected - x64-based Systems
CNA Microsoft Windows Server 2008 R2 Service Pack 1 Server Core Installation affected - x64-based Systems
CNA Microsoft Windows Server 2008 Service Pack 2 affected - 32-bit Systems, x64-based Systems
CNA Microsoft Windows Server 2008 Service Pack 2 Server Core Installation affected - 32-bit Systems, x64-based Systems
CNA Microsoft Windows Server 2012 affected 6.2.9200.0 6.2.9200.23298 custom x64-based Systems
CNA Microsoft Windows Server 2012 Server Core Installation affected 6.2.9200.0 6.2.9200.23298 custom x64-based Systems
CNA Microsoft Windows Server 2012 R2 affected - x64-based Systems
CNA Microsoft Windows Server 2012 R2 Server Core Installation affected - x64-based Systems
CNA Microsoft Windows Server 2016 affected - x64-based Systems
CNA Microsoft Windows Server 2016 Server Core Installation affected - x64-based Systems
CNA Microsoft Windows Server 2019 affected - x64-based Systems
CNA Microsoft Windows Server 2019 Server Core Installation affected - x64-based Systems
CNA Microsoft Windows Server Version 2004 affected - x64-based Systems
CNA Microsoft Windows Server Version 20H2 affected - x64-based Systems
CNA Microsoft Windows Server Version 1909 Server Core Installation affected - x64-based Systems

References

ReferenceSourceLinkTags
Security Update Guide - Microsoft Security Response Center af854a3a-2127-422b-91ae-364da2661108 portal.msrc.microsoft.com Patch, Vendor Advisory
msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26887 [email protected] msrc.microsoft.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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