CVE-2021-26887

CVE-2021-26887 is a high-severity vulnerability in Microsoft Windows 10 with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-59.

Key facts

Description

<p>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.</p> <p>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.</p> <p>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 <strong>FAQ</strong> section of this CVE for configuration guidance.</p>

Frequently asked questions

What is CVE-2021-26887?
<p>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.</p> <p>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.</p> <p>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 <strong>FAQ</strong> section of this CVE for configuration guidance.</p>
How severe is CVE-2021-26887?
CVE-2021-26887 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-26887 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26887?
CVE-2021-26887 primarily affects Microsoft Windows 10. In total, 19 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26887?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-26887 published?
CVE-2021-26887 was published on 2021-03-11 and last updated on 2026-06-17.

References

Affected products (19)

More vulnerabilities in Microsoft Windows 10

All CVEs affecting Microsoft Windows 10 →

Other CWE-59 (Improper Link Resolution Before File Access (Link Following)) vulnerabilities

Browse all CWE-59 (Improper Link Resolution Before File Access (Link Following)) vulnerabilities →