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 full_sessions = prosody.full_sessions;
local bare_sessions = prosody.bare_sessions;
local st = require "util.stanza";
local jid_bare = require "util.jid".bare;
local jid_split = require "util.jid".split;
local user_exists = require "core.usermanager".user_exists;
local function process_to_bare(bare, origin, stanza)
local user = bare_sessions[bare];
local t = stanza.attr.type;
if t == "error" then
return true; -- discard
elseif t == "groupchat" then
origin.send(st.error_reply(stanza, "cancel", "service-unavailable"));
elseif t == "headline" then
if user and stanza.attr.to == bare then
for _, session in pairs(user.sessions) do
if session.presence and session.priority >= 0 then
session.send(stanza);
end
end
end -- current policy is to discard headlines if no recipient is available
else -- chat or normal message
if user then -- some resources are connected
local recipients = user.top_resources;
if recipients then
local sent;
for i=1,#recipients do
sent = recipients[i].send(stanza) or sent;
end
if sent then
return true;
end
end
end
-- no resources are online
local node, host = jid_split(bare);
local ok
if user_exists(node, host) then
ok = module:fire_event('message/offline/handle', {
username = node;
origin = origin,
stanza = stanza,
});
end
if not ok then
origin.send(st.error_reply(stanza, "cancel", "service-unavailable"));
end
end
return true;
end
module:hook("message/full", function(data)
-- message to full JID received
local origin, stanza = data.origin, data.stanza;
local session = full_sessions[stanza.attr.to];
if session and session.send(stanza) then
return true;
else -- resource not online
return process_to_bare(jid_bare(stanza.attr.to), origin, stanza);
end
end, -1);
module:hook("message/bare", function(data)
-- message to bare JID received
local origin, stanza = data.origin, data.stanza;
return process_to_bare(stanza.attr.to or (origin.username..'@'..origin.host), origin, stanza);
end, -1);
module:add_feature("msgoffline");