GOG Galaxy 2.0.0.2 suffers from Missing SSL Certificate Validation. An attacker who controls the local network, DNS, or a proxy can perform a man-in-the-middle (MitM) attack to intercept update requests and replace installer or update packages with malicious files.
The product uses OpenSSL and trusts or uses a certificate without using the SSL_get_verify_result() function to ensure that the certificate satisfies all necessary security requirements.