CVE-2021-28098 in CounterACT
Summary
by MITRE • 04/14/2021
An issue was discovered in Forescout CounterACT before 8.1.4. A local privilege escalation vulnerability is present in the logging function. SecureConnector runs with administrative privileges and writes logs entries to a file in %PROGRAMDATA%\ForeScout SecureConnector\ that has full permissions for the Everyone group. Using a symbolic link allows an attacker to point the log file to a privileged location such as %WINDIR%\System32. The resulting log file adopts the file permissions of the source of the symbolic link (in this case, the Everyone group). The log file in System32 can be replaced and renamed with a malicious DLL for DLL hijacking.
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Analysis
by VulDB Data Team • 04/21/2021
The vulnerability identified as CVE-2021-28098 resides within the Forescout CounterACT security platform, specifically affecting versions prior to 8.1.4. This local privilege escalation flaw stems from improper file permission handling within the SecureConnector component that operates with administrative privileges. The security implications are significant as the vulnerability allows low-privilege attackers to escalate their privileges to system level through a carefully crafted symbolic link attack. The root cause lies in the logging functionality where SecureConnector writes log entries to a directory located at %PROGRAMDATA%\ForeScout SecureConnector\ which is configured with overly permissive permissions granting full access to the Everyone group. This misconfiguration creates an exploitable path where malicious actors can manipulate the logging process to achieve unauthorized system access.
The technical exploitation mechanism involves creating a symbolic link that points the logging destination to a privileged system location such as %WINDIR%\System32. When the SecureConnector process writes to the log file through the symbolic link, the resulting file inherits the permissions of the symbolic link source rather than maintaining the original restrictive permissions. This permission inheritance allows the attacker to replace the target file with a malicious DLL, effectively enabling DLL hijacking. The attack leverages the principle that when a process with elevated privileges creates a file through a symbolic link, the file permissions are determined by the symbolic link's target rather than the original file's permissions. This behavior aligns with common privilege escalation techniques documented in the ATT&CK framework under T1068 for escalation of privileges and T1574 for hijacking.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with a persistent mechanism to maintain access to compromised systems. Once the malicious DLL is placed in the System32 directory, it can execute with system privileges, potentially allowing for complete system compromise. The vulnerability affects organizations using Forescout CounterACT versions before 8.1.4, particularly those where the SecureConnector service runs with administrative privileges. This scenario commonly occurs in enterprise environments where security appliances require elevated permissions to function properly. The attack vector is particularly concerning as it requires minimal privileges to exploit, making it accessible to attackers who may have gained initial access through other means such as phishing or credential theft. Organizations may not immediately detect this compromise as the malicious DLL execution appears legitimate within the system's normal operations.
Mitigation strategies for CVE-2021-28098 focus on both immediate remediation and long-term security hardening. The primary solution involves upgrading to Forescout CounterACT version 8.1.4 or later, which addresses the permission handling issue in the logging function. Additionally, administrators should review and tighten file permissions on the %PROGRAMDATA%\ForeScout SecureConnector\ directory to prevent the Everyone group from having full permissions. The ATT&CK framework suggests implementing process monitoring to detect suspicious file creation patterns and symbolic link usage. Organizations should also consider implementing least privilege principles for the SecureConnector service, ensuring it only has necessary permissions to perform its logging functions. Network segmentation and monitoring of system directories can help detect attempts to place malicious files in privileged locations. Security controls should include regular permission audits and the implementation of application control measures that prevent unauthorized DLL loading. The vulnerability demonstrates the importance of proper permission handling in security applications and aligns with CWE-732, which addresses incorrect permission assignment, making it a critical issue for system administrators to address promptly.