CRLF injection in OpenVPN Access Server

1) CRLF injection

EUVDB-ID: #VU6662

Risk: Medium

CVSSv4.0: 1.2 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2017-5868

CWE-ID: CWE-113 - Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')

Exploit availability: No

Description

The vulnerability allows a remote attacker to inject arbitrary session cookies and gain control over victim's VPN session.

The vulnerability exists due to insufficient sanitization of user-supplied data (e.g. %0A character), passed via URL. A remote attacker can create a specially crafted link, trick the victim into following it and spoof HTTP headers, used by OpenVPN Access Server to authenticate users.

Successful exploitation of the vulnerability may allow an attacker to inject arbitrary cookie values, including session identifier, and gain full access to victim's session.

Exploitation example for injecting victim's session identifier, controlled by the attacker:

https://[host]/__session_start__/%0aSet-Cookie:
openvpn_sess_******=******cf23; Path=/; Secure; HttpOnly

Mitigation

Cybersecurity Help is currently unaware of any official solution to address this vulnerability.

Vulnerable software versions

OpenVPN Access Server: 2.1.0 - 2.1.4

CPE2.3

• cpe:2.3:a:openvpn_net:openvpn_access_server:2.1.0:*:*:*:*:*:*:*
• cpe:2.3:a:openvpn_net:openvpn_access_server:2.1.1:*:*:*:*:*:*:*
• cpe:2.3:a:openvpn_net:openvpn_access_server:2.1.2:*:*:*:*:*:*:*

External links

https://seclists.org/oss-sec/2017/q2/332

Q & A

Can this vulnerability be exploited remotely?

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

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

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