refactor(): fix client Ip vulnerability

context.go

@@ -729,13 +729,13 @@ func (c *Context) ShouldBindBodyWith(obj interface{}, bb binding.BindingBody) (e
 // X-Real-IP and X-Forwarded-For in order to work properly with reverse-proxies such us: nginx or haproxy.
 // Use X-Forwarded-For before X-Real-Ip as nginx uses X-Real-Ip with the proxy's IP.
 func (c *Context) ClientIP() string {
-	if c.engine.ForwardedByClientIP && c.engine.RemoteIPHeaders != nil {
-		for _, header := range c.engine.RemoteIPHeaders {
-			ipChain := filterIPsFromUntrustedProxies(c.requestHeader(header), c.Request, c.engine)
-			if len(ipChain) > 0 {
-				return ipChain[0]
-			}
-		}
+	ip, _, err := net.SplitHostPort(strings.TrimSpace(c.Request.RemoteAddr))
+	if err != nil {
+		return ""
+	}
+	remoteIP := net.ParseIP(ip)
+	if remoteIP == nil {
+		return ""
 	}
 
 	if c.engine.AppEngine {
@@ -744,82 +744,46 @@ func (c *Context) ClientIP() string {
 		}
 	}
 
-	ip, _ := getTransportPeerIPForRequest(c.Request)
+	if c.shouldCheckIPHeaders() {
+		for _, cidr := range c.engine.trustedCIDRs {
+			if cidr.Contains(remoteIP) {
+				for _, headerName := range c.engine.RemoteIPHeaders {
+					ip, valid := validateHeader(c.requestHeader(headerName))
+					if valid {
+						return ip
+					}
+				}
+			}
+		}
+	}
 
-	return ip
+	return remoteIP.String()
 }
 
-func filterIPsFromUntrustedProxies(XForwardedForHeader string, req *http.Request, e *Engine) []string {
-	var items, out []string
-	if XForwardedForHeader != "" {
-		items = strings.Split(XForwardedForHeader, ",")
-	} else {
-		return []string{}
-	}
-	if peerIP, err := getTransportPeerIPForRequest(req); err == nil {
-		items = append(items, peerIP)
-	}
+func (c *Context) shouldCheckIPHeaders() bool {
+	return c.engine.ForwardedByClientIP &&
+		c.engine.RemoteIPHeaders != nil &&
+		len(c.engine.RemoteIPHeaders) > 0 &&
+		c.engine.trustedCIDRs != nil
+}
 
-	for i := len(items) - 1; i >= 0; i-- {
-		item := strings.TrimSpace(items[i])
-		ip := net.ParseIP(item)
+func validateHeader(header string) (clientIP string, valid bool) {
+	if header == "" {
+		return
+	}
+	items := strings.Split(header, ",")
+	for i, ipStr := range items {
+		ipStr = strings.TrimSpace(ipStr)
+		ip := net.ParseIP(ipStr)
 		if ip == nil {
-			return out
+			return "", false
 		}
-
-		out = prependString(ip.String(), out)
-		if !isTrustedProxy(ip, e) {
-			return out
-		}
-		//		out = prependString(ip.String(), out)
-	}
-	return out
-}
-
-func isTrustedProxy(ip net.IP, e *Engine) bool {
-	for _, trustedProxy := range e.TrustedProxies {
-		if _, ipnet, err := net.ParseCIDR(trustedProxy); err == nil {
-			if ipnet.Contains(ip) {
-				return true
-			}
-			continue
-		}
-
-		if proxyIP := net.ParseIP(trustedProxy); proxyIP != nil {
-			if proxyIP.Equal(ip) {
-				return true
-			}
-			continue
-		}
-
-		if addrs, err := e.lookupHost(trustedProxy); err == nil {
-			for _, proxyAddr := range addrs {
-				proxyIP := net.ParseIP(proxyAddr)
-				if proxyIP == nil {
-					continue
-				}
-				if proxyIP.Equal(ip) {
-					return true
-				}
-			}
+		if i == 0 {
+			clientIP = ipStr
+			valid = true
 		}
 	}
-	return false
-}
-
-func prependString(ip string, ipList []string) []string {
-	ipList = append(ipList, "")
-	copy(ipList[1:], ipList)
-	ipList[0] = string(ip)
-	return ipList
-}
-
-func getTransportPeerIPForRequest(req *http.Request) (string, error) {
-	var err error
-	if ip, _, err := net.SplitHostPort(strings.TrimSpace(req.RemoteAddr)); err == nil {
-		return ip, nil
-	}
-	return "", err
+	return
 }
 
 // ContentType returns the Content-Type header of the request.

gin.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"os"
 	"path"
+	"strings"
 	"sync"
 
 	"github.com/gin-gonic/gin/internal/bytesconv"
@@ -118,6 +119,7 @@ type Engine struct {
 	pool             sync.Pool
 	trees            methodTrees
 	maxParams        uint16
+	trustedCIDRs     []*net.IPNet
 }
 
 var _ IRouter = &Engine{}
@@ -312,12 +314,35 @@ func iterate(path, method string, routes RoutesInfo, root *node) RoutesInfo {
 func (engine *Engine) Run(addr ...string) (err error) {
 	defer func() { debugPrintError(err) }()
 
+	trustedCIDRs, err := engine.prepareCIDR()
+	if err != nil {
+		return err
+	}
+	engine.trustedCIDRs = trustedCIDRs
 	address := resolveAddress(addr)
 	debugPrint("Listening and serving HTTP on %s\n", address)
 	err = http.ListenAndServe(address, engine)
 	return
 }
 
+func (engine *Engine) prepareCIDR() ([]*net.IPNet, error) {
+	if engine.TrustedProxies != nil {
+		cidr := make([]*net.IPNet, len(engine.TrustedProxies), 0)
+		for _, trustedProxy := range engine.TrustedProxies {
+			if strings.Contains(trustedProxy, "/") {
+				trustedProxy += "/32"
+			}
+			_, cidrNet, err := net.ParseCIDR(trustedProxy)
+			if err != nil {
+				return cidr, err
+			}
+			cidr = append(cidr, cidrNet)
+		}
+		return cidr, nil
+	}
+	return nil, nil
+}
+
 // RunTLS attaches the router to a http.Server and starts listening and serving HTTPS (secure) requests.
 // It is a shortcut for http.ListenAndServeTLS(addr, certFile, keyFile, router)
 // Note: this method will block the calling goroutine indefinitely unless an error happens.