#VU52479 Improper authentication in OpenVPN for Windows - CVE-2020-15078

Vulnerability identifier: #VU52479

Vulnerability risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2020-15078

CWE-ID: CWE-287

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
OpenVPN for Windows
Client/Desktop applications / Software for system administration

Vendor: OpenVPN

Description

The vulnerability allows a remote attacker to bypass authentication process.

The vulnerability exists due to an error in when processing authentication requests. A remote attacker can bypass authentication and access control channel data on servers configured with deferred authentication, which can be used to potentially trigger further information leaks.

Under certain circumstances an attacker can trick the server using delayed authentication (plugin or management) into returning a PUSH_REPLY before the AUTH_FAILED message, which can possibly be used to gather information about a VPN setup. In combination with "--auth-gen-token" or a user-specific token auth solution it can be possible to get access to a VPN with an otherwise-invalid account.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

OpenVPN for Windows: 2.4.0 - 2.4.10, 2.5.0 - 2.5.1

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External links
https://github.com/OpenVPN/openvpn/releases/tag/v2.4.11
https://github.com/OpenVPN/openvpn/releases/tag/v2.5.2
https://community.openvpn.net/openvpn/wiki/CVE-2020-15078

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.