fix: post policy request security bypass (#16849)

Author: donatello

cmd/api-router.go

@@ -434,8 +434,9 @@ func registerAPIRouter(router *mux.Router) {
 		router.Methods(http.MethodHead).HandlerFunc(
 			collectAPIStats("headbucket", maxClients(gz(httpTraceAll(api.HeadBucketHandler)))))
 		// PostPolicy
-		router.Methods(http.MethodPost).HeadersRegexp(xhttp.ContentType, "multipart/form-data*").HandlerFunc(
-			collectAPIStats("postpolicybucket", maxClients(gz(httpTraceHdrs(api.PostPolicyBucketHandler)))))
+		router.Methods(http.MethodPost).MatcherFunc(func(r *http.Request, _ *mux.RouteMatch) bool {
+			return isRequestPostPolicySignatureV4(r)
+		}).HandlerFunc(collectAPIStats("postpolicybucket", maxClients(gz(httpTraceHdrs(api.PostPolicyBucketHandler)))))
 		// DeleteMultipleObjects
 		router.Methods(http.MethodPost).HandlerFunc(
 			collectAPIStats("deletemultipleobjects", maxClients(gz(httpTraceAll(api.DeleteMultipleObjectsHandler))))).Queries("delete", "")

cmd/auth-handler.go

@@ -25,6 +25,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"io"
+	"mime"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -74,8 +75,11 @@ func isRequestPresignedSignatureV2(r *http.Request) bool {
 
 // Verify if request has AWS Post policy Signature Version '4'.
 func isRequestPostPolicySignatureV4(r *http.Request) bool {
-	return strings.Contains(r.Header.Get(xhttp.ContentType), "multipart/form-data") &&
-		r.Method == http.MethodPost
+	mediaType, _, err := mime.ParseMediaType(r.Header.Get(xhttp.ContentType))
+	if err != nil {
+		return false
+	}
+	return mediaType == "multipart/form-data" && r.Method == http.MethodPost
 }
 
 // Verify if the request has AWS Streaming Signature Version '4'. This is only valid for 'PUT' operation.