Security fixes:

• CVE-2025-13086: Fix memcmp check for the hmac verification in the 3way handshake. This bug renders the HMAC based protection against state exhaustion on receiving spoofed TLS handshake packets in the OpenVPN server inefficient.

Bug fixes:

• fix invalid pointer creation in tls_pre_decrypt() - technically this is a memory over-read issue, in practice, the compilers optimize it away so no negative effects could be observed.
• Windows: in the interactive service, fix the "undo DNS config" handling.
• Windows: in the interactive service, disallow using of "stdin" for the config file, unless the caller is authorized OpenVPN Administrator
• Windows: in the interactive service, change all netsh calls to use interface index and not interface name - sidesteps all possible attack avenues with special characters in interface names.
• Windows: in the interactive service, improve error handling in some "unlikely to happen" paths.