xmlhandlers: Reject XML comments, processing instructions and (if supported by LuaExpat) DTDs. If not supported, log a warning. [Backport of 7cc426988bcc in trunk]

1 files changed, 22 insertions, 0 deletions

diff --git a/core/xmlhandlers.lua b/core/xmlhandlers.lua
index c6684305..6a5cac85 100644
--- a/core/xmlhandlers.lua
+++ b/core/xmlhandlers.lua
@@ -19,6 +19,16 @@ local t_concat = table.concat;
 
 local default_log = require "util.logger".init("xmlhandlers");
 
+-- COMPAT: w/LuaExpat 1.1.0
+local lxp_supports_doctype = pcall(lxp.new, { StartDoctypeDecl = false });
+
+if not lxp_supports_doctype then
+	default_log("warn", "The version of LuaExpat on your system leaves Prosody "
+		.."vulnerable to denial-of-service attacks. You should upgrade to "
+		.."LuaExpat 1.1.1 or higher as soon as possible. See "
+		.."http://prosody.im/doc/depends#luaexpat for more information.");
+end
+
 local error = error;
 
 module "xmlhandlers"
@@ -134,6 +144,18 @@ function init_xmlhandlers(session, stream_callbacks)
 				stanza:up();
 			end
 		end
+
+		local function restricted_handler()
+			cb_error(session, "parse-error", "restricted-xml", "Restricted XML, see RFC 6120 section 11.1.");
+		end
+		
+		if lxp_supports_doctype then
+			xml_handlers.StartDoctypeDecl = restricted_handler;
+		end
+		xml_handlers.Comment = restricted_handler;
+		xml_handlers.StartCdataSection = restricted_handler;
+		xml_handlers.ProcessingInstruction = restricted_handler;
+	
 	return xml_handlers;
 end