OpenVPN Vulnerabilities Disclosed by Microsoft: A Potential Attack Vector
Microsoft recently announced the discovery of four medium-severity security vulnerabilities within the open-source OpenVPN software, which could be exploited in conjunction to enable remote code execution (RCE) and local privilege escalation (LPE). The implications of these flaws are significant, as they may allow attackers to seize full control of affected endpoints, leading to possible data breaches and unauthorized access to sensitive information.
According to Vladimir Tokarev from the Microsoft Threat Intelligence Community, the exploitation of these vulnerabilities could result in severe consequences, including system compromises that affect both individuals and organizations. While the vulnerabilities were unveiled at Black Hat USA 2024, they necessitate user authentication and a sophisticated understanding of OpenVPN’s architecture to be effectively exploited. Importantly, all versions of OpenVPN prior to 2.6.10 and 2.5.10 are vulnerable.
The identified vulnerabilities include: a stack overflow leading to denial of service and local privilege escalation (CVE-2024-27459); unauthorized access to the "\openvpn\service" named pipe in Windows (CVE-2024-24974); a flaw within the plugin mechanism allowing for remote code execution on Windows and local privilege escalation across several platforms such as Android and iOS (CVE-2024-27903); and a memory overflow vulnerability resulting in denial of service in Windows (CVE-2024-1305). Notably, the first three issues originate from a component known as openvpnserv, while the final flaw is associated with the Windows Terminal Access Point (TAP) driver.
These vulnerabilities open a window for attackers who obtain a user’s OpenVPN credentials. Such credentials can be illicitly acquired through various means, including purchasing them on dark web forums, deploying stealer malware, or intercepting network traffic to collect NTLMv2 hashes, subsequently utilizing decryption tools like HashCat or John the Ripper to gain access. Once these credentials are compromised, the attacker can pair vulnerabilities such as CVE-2024-24974 with CVE-2024-27903, or CVE-2024-27459 with CVE-2024-27903, to facilitate successful remote code execution and privilege escalation, crafting an effective attack chain.
Tokarev emphasized the potential for exploiting at least three out of the four vulnerabilities to forge a robust attack mechanism. Techniques such as the Bring Your Own Vulnerable Driver (BYOVD) can be employed after successfully achieving local privilege escalation. This tactic might allow adversaries to disable critical defenses like Protect Process Light (PPL) for essential processes such as Microsoft Defender. By undermining these security measures, attackers can manipulate vital system functions, thus solidifying their control while evading detection.
The vulnerabilities detailed can be correlated with tactics outlined in the MITRE ATT&CK Framework, particularly under areas such as initial access, privilege escalation, and defense evasion. Understanding these frameworks is essential in the realm of cybersecurity, as they provide insights into potential adversary behavior and strategies.
Business leaders and IT professionals should remain vigilant in light of these discoveries, ensuring their organizations are not only aware of the vulnerabilities present in OpenVPN but also actively patching affected systems. As the cybersecurity landscape continues to evolve, awareness and proactive measures are crucial in safeguarding sensitive data and maintaining organizational integrity.
