#VU7165 MitM attack in OpenVPN for Windows - CVE-2017-7520

Vulnerability identifier: #VU7165

Vulnerability risk: Low

CVSSv4.0: 1 [CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2017-7520

CWE-ID: CWE-200

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 perform a denial of service (DoS) attack or obtain potentially sensitive client's information.

If clients use a HTTP proxy with NTLM authentication (i.e. "--http-proxy <server> <port> [<authfile>|'auto'|'auto-nct'] ntlm2"), a man-in-the-middle attacker between the client and the proxy can cause the client to crash or disclose at most 96 bytes of stack memory. The disclosed stack memory is likely to contain the proxy password.

Mitigation
Update OpenVPN to version 2.4.3.

Vulnerable software versions

OpenVPN for Windows: 2.4.0 - 2.4.2

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External links
https://community.openvpn.net/openvpn/wiki/ChangesInOpenvpn24

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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.