Refuse to publish things that aren't strings, things will blow up when anyone tries to retrieve them!

deps/rabbitmq_management/src/rabbit_mgmt_wm_exchange_publish.erl

@@ -47,6 +47,10 @@ do_it(ReqData, Context) ->
     rabbit_mgmt_util:with_decode(
       [routing_key, properties, payload, payload_encoding], ReqData, Context,
       fun([RoutingKey, Props0, Payload0, Enc], _) ->
+              case Payload0 of
+                  P when is_binary(P) -> ok;
+                  _                   -> throw({error, payload_not_string})
+              end,
               rabbit_mgmt_util:with_channel(
                 VHost, ReqData, Context,
                 fun (Ch) ->

deps/rabbitmq_management/test/src/rabbit_mgmt_test_http.erl

@@ -860,6 +860,12 @@ publish_fail_test() ->
             {payload,          <<"Hello world">>},
             {payload_encoding, <<"string">>}],
     http_post("/exchanges/%2f/amq.default/publish", Msg2, ?BAD_REQUEST),
+    Msg3 = [{exchange,         <<"">>},
+            {routing_key,      <<"myqueue">>},
+            {properties,       []},
+            {payload,          [<<"not a string">>]},
+            {payload_encoding, <<"string">>}],
+    http_post("/exchanges/%2f/amq.default/publish", Msg3, ?BAD_REQUEST),
     http_delete("/users/myuser", ?NO_CONTENT),
     ok.