I'm a little surprised the OpenSSL API doesn't force you to consider this by default, but indeed it does not: https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html...

> On session establishment, by default, no peer credentials verification is done. This must be explicitly requested, typically using SSL_CTX_set_verify(3).

Aside: According to those docs, SSLv23_client_method() is deprecated.