CVE-2021-26887 : Vulnerability Insights and Analysis

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.

Understanding CVE-2021-26887

This CVE relates to an elevation of privilege vulnerability in Microsoft Windows associated with Folder Redirection, affecting various versions of the Windows operating system.

What is CVE-2021-26887?

CVE-2021-26887 is an elevation of privilege vulnerability in Microsoft Windows, specifically related to Folder Redirection settings via Group Policy. The vulnerability allows an attacker to redirect another user's personal data to a created folder, exploiting the co-location of folder redirection file servers with Terminal servers.

The Impact of CVE-2021-26887

The successful exploitation of this vulnerability could lead to an attacker redirecting personal data of users to unauthorized locations, compromising confidentiality and data integrity.

Technical Details of CVE-2021-26887

This section provides more in-depth technical details about the vulnerability.

Vulnerability Description

The vulnerability arises when Folder redirection is enabled via Group Policy, allowing attackers to redirect personal data to unauthorized folders.

Affected Systems and Versions

Various versions of Windows operating systems, including Windows 10, Windows Server, and older versions, are affected by this vulnerability.

Exploitation Mechanism

Attackers exploit the vulnerability by creating new folders and junction points, tricking Folder Redirection to copy personal data to unauthorized locations.

Mitigation and Prevention

It is crucial to take immediate steps to address and prevent the exploitation of CVE-2021-26887.

Immediate Steps to Take

Reconfigure Folder Redirection settings with Offline files and restrict permissions to prevent unauthorized data redirection.

Long-Term Security Practices

Implement security best practices, regularly review configurations, and educate users on data security to prevent similar exploits.

Patching and Updates

Updating affected Windows Servers will not address this vulnerability. Refer to the FAQ section for detailed configuration guidance.