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Full vulnerability report · 2021
CVE-2021-26887High confidence

Microsoft Windows Folder Redirection Elevation of Privilege Vulnerability

Microsoft · Windows 10 Version 1507

7.8HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Medium, lowered one band.downgradedsince 19 Aug 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 1.06% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Microsoft Windows 10 Version 1507 and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-13671

No EUVD known-exploited evidence

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.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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.

What

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.

Why

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.

What

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.

Why

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
local access → Improper Link Resolution Before File Access ('Link Following') → gain additional privileges
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-59 ↗

CWE-59: Improper Link Resolution Before File Access ('Link Following'). The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
Privilege escalationCWE-59
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2021-13671Official EUVD mapping

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.

Official EUVD record ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210317Security Bulletin 17 Mar 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 17 Mar 2021, published on 17 March 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-181Multiples vulnérabilités dans Microsoft Windows

d?id=CVE-2021-26877 Référence CVE CVE-2021-26878 https://www.cve.org/CVERecord?id=CVE-2021-26878 Référence CVE CVE-2021-26879 https://www.cve.org/CVERecord?id=CVE-2021-26879 Référence CVE CVE-2021-26880 https://www.cve.org/CVERecord?id=CVE-2021-26880 Référence CVE CVE-2021-26881 https://www.cve.org/CVERecord?id=CVE-2021-26881 Référence CVE CVE-2021-26882 https://www.cve.org/CVERecord?id=CVE-2021-26882 Référence CVE CVE-2021-26884 https://www.cve.org/CVERecord?id=CVE-2021-26884 Référence CVE CVE-2021-26885 https://www.cve.org/CVERecord?id=CVE-2021-26885 Référence CVE CVE-2021-26886 https://www.cve.org/CVERecord?id=CVE-2021-26886 Référence CVE CVE-2021-26887 https://www.cve.org/CVERecord?id=CVE-2021-26887 Référence CVE CVE-2021-26889 https://www.cve.org/CVERecord?id=CVE-2021-26889 Référence CVE CVE-2021-26890 https://www.cve.org/CVERecord?id=CVE-2021-26890 Référence CVE CVE-2021-26891 https://www.cve.org/CVERecord?id=CVE-2021-26891 Référence CVE CVE-2021-26892 https://www.cve.org/CVERecord?id=CVE-2021-26892 Référence CVE CVE-2021-26893 https://www.cve.org/CVERecord?id=CVE-2021-26893 Référence CVE CVE-2021-26894 https://www.cve.org/CVERecord?id=CVE-2021-26894 Référence CVE CVE-2021-26895 https://www.cve.org/CVERecord?id=CVE-2021-26895 Référence CVE CVE-2021-26896 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001226複数の Microsoft Windows 製品における権限を昇格される脆弱性

複数の Microsoft Windows 製品には、Microsoft Windows フォルダリダイレクトに不備があるため、権限を昇格される脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5282MS 3월 보안 위협에 따른 정기 보안 업데이트 권고

Studio Code용 원격 개발 확장 원격 코드 실행 취약성 CVE-2021-27082 Visual Studio Code용 Microsoft Quantum 개발 키트 원격 코드 실행 취약성 CVE-2021-27081 Visual Studio Code ESLint 확장 원격 코드 실행 취약성 CVE-2021-27060 Visual Studio Code 원격 코드 실행 취약성 Windows Admin Center CVE-2021-27066 Windows 관리 센터 보안 기능 우회 취약성 CVE-2021-26891 Windows 컨테이너 실행 에이전트 권한 상승 취약성 CVE-2021-26865 Windows 컨테이너 실행 에이전트 권한 상승 취약성 CVE-2021-24095 DirectX 권한 상승 취약성 CVE-2021-24090 Windows 오류 보고 권한 상승 취약성 CVE-2021-26901 Windows 이벤트 추적 권한 상승 취약성 CVE-2021-26898 Windows 이벤트 추적 권한 상승 취약성 CVE-2021-26872 Windows 이벤트 추적 권한 상승 취약성 CVE-2021-24107 Windows 이벤트 추적 정보 유출 취약성 CVE-2021-26892 Windows 확장 가능 펌웨어 인터페이스 보안 기능 우회 취약성 CVE-2021-26887 Microsoft Windows 폴더 리디렉션 권한 상승 취약성 CVE-2021-26862 Windows Installer 권한 상승 취약성 CVE-2021-26881 Windows 미디어 파운데이션 원격 코드 실행 취약성 CVE-2021-26874 Windows 오버레이 필터 권한 상승 취약성 CVE-2021-26860 Windows 앱-V 오버레이 필터 권한 상승 취약성 CVE-2021-26878 Windows 인쇄 스풀러 권한 상승 취약성 CVE-2021-1640 Windows 인쇄 스풀러 권한 상승 취약성 CVE-2021-26870 Windows 예상 파일 시스템 권한 상승 취약성 CVE-2021-26864 Windows 가상 레지스트리 공급자 권한 상승 취약성 CVE-2021-26882 원격 액세스 API 권한 상승 취약성 CVE-2021-26880 저장소 공간 컨트롤러 권한 상승 취약성 CVE-2021-27070 Windows 10 업데이트 길잡이 권한 상승 취약성 CVE-2021-26889 Windows 업데이트 스택 권한 상승 취약성 CVE-2021-26866 Windows Update Medic Service 권한 상승 취약성 CVE-2021-1729 Windows 업데이트 스택 설정 권한 상승 취약성 CVE-2021-26899

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 11 Mar 2021 · Last source change 19 Aug 2026, 16:30 UTC · CWE-59 · Improper Link Resolution Before File Access ('Link Following')

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-13671
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceNIST NVD
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added remediation: portal.msrc.microsoft.com/CVE-2021-26887; removed patch: msrc.microsoft.com/CVE-2021-26887; removed remediation: msrc.microsoft.com/CVE-2021-26887.
    Before
    patch: msrc.microsoft.com/CVE-2021-26887 · patch: portal.msrc.microsoft.com/CVE-2021-26887 · remediation: msrc.microsoft.com/CVE-2021-26887
    After
    patch: portal.msrc.microsoft.com/CVE-2021-26887 · remediation: portal.msrc.microsoft.com/CVE-2021-26887
    portal.msrc.microsoft.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added patch: msrc.microsoft.com/CVE-2021-26887; added remediation: msrc.microsoft.com/CVE-2021-26887; removed remediation: portal.msrc.microsoft.com/CVE-2021-26887.
    Before
    patch: portal.msrc.microsoft.com/CVE-2021-26887 · remediation: portal.msrc.microsoft.com/CVE-2021-26887
    After
    patch: msrc.microsoft.com/CVE-2021-26887 · patch: portal.msrc.microsoft.com/CVE-2021-26887 · remediation: msrc.microsoft.com/CVE-2021-26887
    msrc.microsoft.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    N/A · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    - · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-13671↗Patch or update reference↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-26887 · cve.blacktree.nl