RubyGems before 1.8.23 can redirect HTTPS connections to HTTP, which makes it easier for remote attackers to observe or modify a gem during installation via a man-in-the-middle attack.
RubyGems < 1.8.23 - Man-in-the-Middle Attack via Unverified SSL Certificate
RubyGems before 1.8.23 does not verify an SSL certificate, which allows remote attackers to modify a gem during installation via a man-in-the-middle attack.