Echo is a Go web framework. From 4.0.0 until 5.1.0, Context.RealIP falls back to client-supplied X-Forwarded-For or X-Real-IP values when Echo.IPExtractor is unset, and the default RateLimiter uses that result as its client identifier. A remote attacker can rotate arbitrary forwarded-address values to obtain new rate-limit buckets and bypass IP-based throttling used for controls such as brute-force or request-volume protection. This issue is fixed in Echo v5.1.0.