CVE-2020-15074 in Access Server
Summary
by MITRE
OpenVPN Access Server older than version 2.8.4 generates new user authentication tokens instead of reusing exiting tokens on reconnect making it possible to circumvent the initial token expiry timestamp.
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Analysis
by VulDB Data Team • 10/30/2020
The vulnerability identified as CVE-2020-15074 affects OpenVPN Access Server versions prior to 2.8.4 and represents a significant authentication flaw that undermines the security of user sessions. This issue stems from improper token management within the authentication subsystem where the system fails to properly handle token reuse during reconnect operations. The flaw specifically manifests when users establish new connections to the VPN service, causing the server to generate fresh authentication tokens rather than utilizing existing valid tokens that should remain active. This behavior creates a window of opportunity for attackers to exploit the authentication mechanism and potentially extend the validity of compromised sessions beyond their intended expiration time.
The technical implementation of this vulnerability resides in the server-side token handling logic that governs how authentication credentials are managed during connection lifecycle events. When a user reconnects to the OpenVPN Access Server, the system should validate existing tokens and maintain their expiration timestamps to ensure proper session management. However, the flawed implementation causes the server to generate new tokens with fresh expiration timers, effectively resetting the session validity period. This design flaw violates fundamental security principles regarding session management and token lifecycle control. The vulnerability is classified under CWE-284 Access Control, specifically related to improper access control mechanisms within authentication systems, and aligns with ATT&CK technique T1566 Credential Stuffing and T1550 Use of Privileged Accounts.
The operational impact of this vulnerability extends beyond simple session management issues and creates real security risks for organizations relying on OpenVPN Access Server for remote access. Attackers who gain access to valid authentication tokens can exploit this behavior to extend the validity of their compromised sessions indefinitely, effectively bypassing time-based security controls. This creates persistent access vectors that could remain undetected for extended periods, particularly in environments where users reconnect frequently or maintain long-running sessions. The vulnerability becomes more pronounced in scenarios where session timeouts are configured to enforce regular re-authentication, as the system's behavior directly contradicts these security controls. Organizations may experience unauthorized access to sensitive resources, potential data exfiltration, and increased risk of privilege escalation attacks that leverage the extended session validity periods.
Mitigation strategies for CVE-2020-15074 primarily focus on immediate patch management and operational security improvements. Organizations should prioritize upgrading to OpenVPN Access Server version 2.8.4 or later, which contains the necessary fixes to properly handle token reuse during reconnect operations. Additionally, security teams should implement monitoring for unusual authentication patterns, particularly repeated connection attempts that might indicate exploitation attempts. Network segmentation and multi-factor authentication should be enforced to reduce the impact of any potential compromise, while regular security audits should verify that token management configurations align with security best practices. The vulnerability highlights the importance of proper session management in authentication systems and underscores the need for comprehensive testing of authentication flows during system updates and configuration changes.