resolv-replace is a Ruby helper that redirects socket-based name resolution to Ruby’s own Resolv library instead of the operating system’s default resolver. In practice, it changes how calls that look up hostnames are handled, so the application’s DNS behavior is controlled by Ruby code.
This matters because DNS often sits on a trust boundary. Applications use name resolution for outbound allowlists, hostname validation, redirect checks, and other security decisions. If a program relies on resolv-replace, then bugs in Ruby’s resolver can affect both availability and policy enforcement. An attacker who can influence DNS replies may trigger excessive resource use, crashes, or mismatches between what the application believes it validated and what actually gets resolved. Defenders should know whether this helper is enabled, patch the bundled resolver, and test any security logic that depends on DNS results.