CVE-2018-10381 in TunnelBear
Summary
by MITRE
TunnelBear 3.2.0.6 for Windows suffers from a SYSTEM privilege escalation vulnerability through the "TunnelBearMaintenance" service. This service establishes a NetNamedPipe endpoint that allows arbitrary installed applications to connect and call publicly exposed methods. The "OpenVPNConnect" method accepts a server list argument that provides attacker control of the OpenVPN command line. An attacker can specify a dynamic library plugin that should run for every new VPN connection attempt. This plugin will execute code in the context of the SYSTEM user.
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Analysis
by VulDB Data Team • 01/31/2020
The vulnerability identified as CVE-2018-10381 represents a critical privilege escalation flaw in TunnelBear version 3.2.0.6 for Windows operating systems. This issue stems from the improper implementation of the TunnelBearMaintenance service which operates with elevated SYSTEM privileges. The service creates a named pipe endpoint using the NetNamedPipe protocol that exposes publicly accessible methods to any installed application on the system. This design flaw directly violates the principle of least privilege and creates an attack surface that allows malicious actors to leverage the service for unauthorized code execution. The vulnerability manifests through the OpenVPNConnect method which accepts a server list parameter that can be manipulated by attackers to inject malicious dynamic library plugins. This particular implementation pattern aligns with CWE-264, which addresses permissions, privileges, and access controls, specifically focusing on inadequate privilege management. The flaw essentially provides a pathway for local privilege escalation by allowing any application to invoke methods that execute code under the SYSTEM context.
The technical exploitation of this vulnerability occurs through the manipulation of the OpenVPN command line interface via the server list argument passed to the OpenVPNConnect method. When an attacker specifies a dynamic library plugin within this parameter, the OpenVPN client will execute the malicious plugin code with the privileges of the currently running process, which in this case is the TunnelBearMaintenance service operating as SYSTEM. This creates a direct code execution chain where arbitrary code can be executed with the highest possible privileges on the target system. The attack vector leverages the Windows named pipe communication mechanism and the OpenVPN plugin architecture, combining these elements to achieve unauthorized privilege escalation. The vulnerability demonstrates a classic case of insecure inter-process communication where a service with elevated privileges exposes methods without proper authentication or authorization checks, making it susceptible to exploitation by local attackers. This type of attack pattern is documented in the ATT&CK framework under privilege escalation techniques, specifically targeting service execution and dynamic link library injection methods.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete system compromise. An attacker with local access can leverage this flaw to gain SYSTEM-level control over the affected machine, enabling them to modify system files, install persistent backdoors, access sensitive data, and potentially pivot to other systems within the network. The vulnerability affects all Windows systems running TunnelBear 3.2.0.6 where the service is installed and running, making it particularly dangerous in enterprise environments where multiple users might have local access to systems. The exploitability of this vulnerability is relatively straightforward since it requires only local system access and does not depend on network connectivity or complex attack chains. Once exploited, the attacker gains the ability to perform any action that the SYSTEM account can perform, including modifying registry entries, installing malicious software, accessing encrypted data, and potentially escalating further to domain-level privileges if the compromised system is part of a domain environment.
Mitigation strategies for CVE-2018-10381 should focus on immediate remediation through software updates from TunnelBear, as the vendor has released patches to address this vulnerability. Organizations should also implement network segmentation and access controls to limit local user privileges and prevent unauthorized software installation. The service should be configured with appropriate access controls using Windows security descriptors to restrict which users or processes can connect to the named pipe endpoint. System administrators should monitor for unauthorized applications that might attempt to connect to the TunnelBearMaintenance service and implement application whitelisting policies to prevent arbitrary code execution. Additionally, the vulnerability highlights the importance of secure service design practices, particularly regarding inter-process communication and privilege management, which should be enforced through regular security audits and code reviews. The remediation process should include disabling the vulnerable service if immediate updates are not possible, while also conducting thorough vulnerability assessments to identify other services that might be susceptible to similar privilege escalation flaws. Organizations should also consider implementing endpoint detection and response solutions to monitor for suspicious named pipe connections and dynamic library loading activities that could indicate exploitation attempts.