Echo is a Go web framework. From 4.0.0 until 5.4.0, the Proxy middleware can preserve an attacker-supplied X-Real-IP header and forward it to an upstream service when Echo.IPExtractor is not configured. A remote client can therefore make upstream services receive a spoofed client address, undermining IP-based access controls, rate limiting, audit logging, or geographic restrictions that trust Echo's forwarded identity. This issue is fixed in Echo 5.4.0.

Affected: Go: github.com/labstack/echo/v5, Go: github.com/labstack/echo/v4

## Summary

The Echo proxy middleware (`middleware/proxy.go`) preserves an incoming `X-Real-IP` header verbatim and forwards it to the upstream service when `Echo#IPExtractor` is not configured — which is the default. Because any HTTP client can supply an arbitrary `X-Real-IP` value, an attacker can cause Echo to relay a spoofed client IP address to every upstream service behind the proxy, undermining upstream IP-based access controls, rate limiting, audit logging, and geo-restriction.

## Affected Component

- `middleware/proxy.go` — `ProxyConfig.ToMiddleware()`, header-rewriting block (lines 351–355)

## Description

### The header-preservation condition passes spoofed values to upstream

`ProxyConfig.ToMiddleware()` (`proxy.go:338-405`) prepares forwarding headers before dispatching each request. The `X-Real-IP` rewrite logic at lines 351-355 reads:

```go // proxy.go:351-355 // Basically it's not good practice to unconditionally pass incoming x-real-ip header to upstream. // However, for backward compatibility, legacy behavior is preserved unless you configure Echo#IPExtractor. if req.Header.Get(echo.HeaderXRealIP) == "" || c.Echo().IPExtractor != nil { req.Header.Set(echo.HeaderXRealIP, c.RealIP()) } ```

The condition is `TRUE` (and therefore overwrites the header with a derived value) only when: - The header is absent — `req.Header.Get(echo.HeaderXRealIP) == ""`; **or** - `IPExtractor` is explicitly configured — `c.Echo().IPExtractor != nil`

The condition is `FAL…

Affected: Ubuntu:20.04:LTS: golang-github-labstack-echo.v2, Ubuntu:20.04:LTS: golang-github-labstack-echo.v3, Ubuntu:22.04:LTS: golang-github-labstack-echo, Ubuntu:22.04:LTS: golang-github-labstack-echo.v2, Ubuntu:22.04:LTS: golang-github-labstack-echo.v3, Ubuntu:24.04:LTS: golang-github-labstack-echo, Ubuntu:26.10: golang-github-labstack-echo, Ubuntu:26.04:LTS: golang-github-labstack-echo

Echo is a Go web framework. From 4.0.0 until 5.4.0, the Proxy middleware can preserve an attacker-supplied X-Real-IP header and forward it to an upstream service when Echo.IPExtractor is not configured. A remote client can therefore make upstream services receive a spoofed client address, undermining IP-based access controls, rate limiting, audit logging, or geographic restrictions that trust Echo's forwarded identity. This issue is fixed in Echo 5.4.0.