Echo is a Go web framework. From 5.0.0 until 5.4.1, Echo v5's ExtractIPFromRealIPHeader validates whether the client-supplied X-Real-IP value belongs to a trusted range instead of validating the direct network peer. A client reaching Echo directly, or through a proxy that preserves the header, can supply a loopback or private address and have Context.RealIP return that spoofed identity. Applications using the extractor for IP allowlists, rate limiting, audit logs, or forwarding headers can consequently trust an attacker-controlled address; the default direct extractor and Echo v4 are unaffected. This issue is fixed in 5.4.1.