An issue was discovered in OpenVPN 2.4.x before 2.4.9. 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.
bugzilla.suse.com/show_bug.cgi?id=1169925
community.openvpn.net/openvpn/ticket/1272
github.com/OpenVPN/openvpn/commit/37bc691e7d26ea4eb61a8a434ebd7a9ae76225ab
lists.debian.org/debian-lts-announce/2022/05/msg00002.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FGHHV4YZANZW45KZTJJGVGPFMSXYRCKZ/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JII7RYYYRBPQNEGGVSOXCM7JUZ43T3VH/
patchwork.openvpn.net/patch/1079/
security-tracker.debian.org/tracker/CVE-2020-11810