Check status codes that profile handler returns

changelog.d/8580.bugfix

@@ -0,0 +1 @@
+Fix a bug where Synapse would blindly forward bad responses from federation to clients when retrieving profile information.

synapse/handlers/profile.py

@@ -89,6 +89,14 @@ async def get_profile(self, user_id):
             except RequestSendFailed as e:
                 raise SynapseError(502, "Failed to fetch profile") from e
             except HttpResponseException as e:
+                if e.code < 500 and e.code != 404:
+                    # Other codes are not allowed in c2s API
+                    logger.error(
+                        "Server replied with wrong response: %s %s", e.code, e.msg
+                    )
+                    # Change to 500 not to confuse clients
+                    e.code = 500
+                    e.msg = "Remote server replied: {} {}".format(e.code, e.msg)
                 raise e.to_synapse_error()
 
     async def get_profile_from_cache(self, user_id):