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ReviewHigh

CVE-2021-26887

Microsoft Windows 10 Version 1507, Windows 10 Version 1607, Windows 10 Version 1803

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 p...

CVSS
7.8
EPSS
1.06%
62.1% percentile
CISA KEV
Not listed
Published
2021.03.12
PRIORITY ASSESSMENT

Review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability1.06%
Technical severityCVSS 7.8

Vulnerability overview

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 p...

Affected product and versions

Product
Microsoft Windows 10 Version 1507, Windows 10 Version 1607, Windows 10 Version 1803
Affected versions
>= 6.2.9200.0 < 6.2.9200.23298, 20h2, 1607, 1803, 1809, 1909, 2004, r2
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Microsoft Windows 10 Version 1507, Windows 10 Version 1607, Windows 10 Version 1803 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-59