CVE-2026-78221 - Windows openvpnserv buffer overread via UTF8 IDN NRPT domains

OpenVPN 2.x on Windows allows attackers to achieve a buffer overread in openvpnserv because an incorrect NRPT domains size was passed on, which becomes visible when IDN domains with UTF8 encoding are involved.

OpenVPN version 2.7_alpha1 through 2.7.6 are affected. This is fixed in version 2.7.7.

CVE Record: CVE-2026-78221

Github:

• OpenVPN/openvpn-private-issues#162

Release notes:

• openvpn-2.7.7

Reported-By: BreachX Zero Day Labs (using Typhon AI Mil v2)