util.xml: Do not allow doctypes, comments or processing instructions
Yes. This is as bad as it sounds. CVE pending.
In Prosody itself, this only affects mod_websocket, which uses util.xml
to parse the <open/> frame, thus allowing unauthenticated remote DoS
using Billion Laughs. However, third-party modules using util.xml may
also be affected by this.
This commit installs handlers which disallow the use of doctype
declarations and processing instructions without any escape hatch. It,
by default, also introduces such a handler for comments, however, there
is a way to enable comments nontheless.
This is because util.xml is used to parse human-facing data, where
comments are generally a desirable feature, and also because comments
are generally harmless.
-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
local st = require "util.stanza"
local private_storage = module:open_store("private", "map");
module:add_feature("jabber:iq:private");
module:hook("iq/self/jabber:iq:private:query", function(event)
local origin, stanza = event.origin, event.stanza;
local query = stanza.tags[1];
if #query.tags ~= 1 then
origin.send(st.error_reply(stanza, "modify", "bad-format"));
return true;
end
local tag = query.tags[1];
local key = tag.name..":"..tag.attr.xmlns;
if stanza.attr.type == "get" then
local data, err = private_storage:get(origin.username, key);
if data then
origin.send(st.reply(stanza):query("jabber:iq:private"):add_child(st.deserialize(data)));
elseif err then
origin.send(st.error_reply(stanza, "wait", "internal-server-error", err));
else
origin.send(st.reply(stanza):add_child(query));
end
return true;
else -- stanza.attr.type == "set"
local data;
if #tag ~= 0 then
data = st.preserialize(tag);
end
-- TODO delete datastore if empty
local ok, err = private_storage:set(origin.username, key, data);
if not ok then
origin.send(st.error_reply(stanza, "wait", "internal-server-error", err));
return true;
end
origin.send(st.reply(stanza));
return true;
end
end);