Denial of service in OpenVPN

1) Resource management error

EUVDB-ID: #VU27616

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 - Resource Management Errors

Exploit availability: No

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

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

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.