Vulnerability identifier: #VU27616

Vulnerability risk: Low

CVSSv3.1: 3.2 [CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L/E:U/RL:O/RC:C]

CVE-ID: CVE-2020-11810

CWE-ID: CWE-399

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
OpenVPN
Server applications / Remote access servers, VPN

Vendor: openvpn.net

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to improper management of internal resources within the application that allows a timing attack to be carried out against OpenVPN clients.

An attacker can inject a data channel v2 (P_DATA_V2) packet using a victim's peer-id. Normally such packets are dropped, but if this packet arrives before the data channel crypto parameters have been initialized, the victim's connection will be dropped. This requires careful timing due to the small time window (usually within a few seconds) between the victim client connection starting and the server PUSH_REPLY response back to the client. This attack will only work if Negotiable Cipher Parameters (NCP) is in use.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

OpenVPN: 2.4.0 - 2.4.8

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External links
http://bugzilla.suse.com/show_bug.cgi?id=1169925
http://community.openvpn.net/openvpn/ticket/1272
http://github.com/OpenVPN/openvpn/commit/37bc691e7d26ea4eb61a8a434ebd7a9ae76225ab
http://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/FGHHV4YZANZW45KZTJJGVGPFMSXYRCKZ/
http://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/JII7RYYYRBPQNEGGVSOXCM7JUZ43T3VH/
http://patchwork.openvpn.net/patch/1079/
http://security-tracker.debian.org/tracker/CVE-2020-11810

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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.