# CVE-2026-81738 - Windows single-byte overflow in write_dhcp_search_str() temp buffer

OpenVPN 2.x on Windows allows attackers to overflow a temporary buffer by a single byte via suitably crafted DHCP options, due to an off-by-one in the buffer guard in `write_dhcp_search_str()`.

OpenVPN version 2.5.0 through 2.7.6 are affected. This is fixed in version 2.7.7.

CVE Record: [CVE-2026-81738](https://www.cve.org/CVERecord?id=CVE-2026-81738)

Github:
* [OpenVPN/openvpn-private-issues#165](https://github.com/OpenVPN/openvpn-private-issues/issues/165)

Release notes:
* [openvpn-2.7.7](https://community.openvpn.net/ReleaseHistory#openvpn-277-released-3-september-2026)

Reported-By: Andre Kropp (Nexory) and ChinhNguyen