CVE-2018-10066 in MikroTik
Summary
by MITRE
An issue was discovered in MikroTik RouterOS 6.41.4. Missing OpenVPN server certificate verification allows a remote unauthenticated attacker capable of intercepting client traffic to act as a malicious OpenVPN server. This may allow the attacker to gain access to the client's internal network (for example, at site-to-site tunnels).
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Analysis
by VulDB Data Team • 01/24/2020
The vulnerability identified as CVE-2018-10066 represents a critical security flaw in MikroTik RouterOS version 6.41.4 that fundamentally undermines the integrity of OpenVPN server implementations. This weakness stems from insufficient certificate verification mechanisms within the OpenVPN server component, creating a dangerous attack vector for remote adversaries who can intercept network traffic between clients and servers. The flaw operates at the core of cryptographic trust establishment processes, where proper certificate validation should prevent man-in-the-middle attacks but fails to do so in this specific implementation.
The technical nature of this vulnerability aligns with CWE-295, which addresses improper certificate validation, and represents a failure in the certificate chain validation process that should occur during the OpenVPN handshake. When an attacker successfully intercepts client traffic, they can exploit this missing verification step to present a fraudulent certificate that appears legitimate to the client. This allows the malicious actor to establish a false OpenVPN server session and decrypt traffic flowing through the tunnel, effectively breaking the confidentiality guarantees that OpenVPN is designed to provide. The attack requires only network interception capabilities and does not necessitate authentication credentials from the target system.
The operational impact of this vulnerability extends beyond simple data interception to potentially enable full network compromise through site-to-site tunnel exploitation. An attacker who successfully impersonates the legitimate OpenVPN server can gain access to internal network resources that the client would normally be authorized to reach, including corporate networks, internal services, and sensitive data repositories. This creates a significant risk for organizations that rely on OpenVPN for secure remote access or site-to-site connectivity, as the attacker essentially gains the same network privileges that legitimate users would possess. The vulnerability is particularly dangerous because it can be exploited without authentication, making it accessible to any attacker who can monitor the network traffic between client and server.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to MikroTik RouterOS versions that contain the patched certificate verification mechanisms, implementing additional network monitoring to detect anomalous OpenVPN traffic patterns, and potentially disabling OpenVPN services until proper updates are applied. The ATT&CK framework categorizes this as a credential access technique through network sniffing and man-in-the-middle attacks, with potential lateral movement capabilities once the attacker gains access to internal network resources. Security teams should also consider implementing certificate pinning mechanisms and enhanced network segmentation to limit the potential damage from successful exploitation, while monitoring for unusual certificate validation behaviors that might indicate an active attack.