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.
-- Copyright (C) 2016-2018 Kim Alvefur
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
module:depends"csi"
local jid = require "util.jid";
local st = require "util.stanza";
local dt = require "util.datetime";
local new_queue = require "util.queue".new;
local function new_pump(output, ...)
-- luacheck: ignore 212/self
local q = new_queue(...);
local flush = true;
function q:pause()
flush = false;
end
function q:resume()
flush = true;
return q:flush();
end
local push = q.push;
function q:push(item)
local ok = push(self, item);
if not ok then
q:flush();
output(item, self);
elseif flush then
return q:flush();
end
return true;
end
function q:flush()
local item = self:pop();
while item do
output(item, self);
item = self:pop();
end
return true;
end
return q;
end
local queue_size = module:get_option_number("csi_queue_size", 256);
module:hook("csi-is-stanza-important", function (event)
local stanza = event.stanza;
if not st.is_stanza(stanza) then
return true;
end
local st_name = stanza.name;
if not st_name then return false; end
local st_type = stanza.attr.type;
if st_name == "presence" then
if st_type == nil or st_type == "unavailable" then
return false;
end
return true;
elseif st_name == "message" then
if st_type == "headline" then
return false;
end
if stanza:get_child("sent", "urn:xmpp:carbons:2") then
return true;
end
local forwarded = stanza:find("{urn:xmpp:carbons:2}received/{urn:xmpp:forward:0}/{jabber:client}message");
if forwarded then
stanza = forwarded;
end
if stanza:get_child("body") then
return true;
end
if stanza:get_child("subject") then
return true;
end
if stanza:get_child("encryption", "urn:xmpp:eme:0") then
return true;
end
if stanza:get_child(nil, "urn:xmpp:jingle-message:0") then
return true;
end
return false;
end
return true;
end, -1);
module:hook("csi-client-inactive", function (event)
local session = event.origin;
if session.pump then
session.pump:pause();
else
local bare_jid = jid.join(session.username, session.host);
local send = session.send;
session._orig_send = send;
local pump = new_pump(session.send, queue_size);
pump:pause();
session.pump = pump;
function session.send(stanza)
if session.state == "active" or module:fire_event("csi-is-stanza-important", { stanza = stanza, session = session }) then
pump:flush();
send(stanza);
else
if st.is_stanza(stanza) and stanza.attr.xmlns == nil and stanza.name ~= "iq" then
stanza = st.clone(stanza);
stanza:add_direct_child(st.stanza("delay", {xmlns = "urn:xmpp:delay", from = bare_jid, stamp = dt.datetime()}));
end
pump:push(stanza);
end
return true;
end
end
end);
module:hook("csi-client-active", function (event)
local session = event.origin;
if session.pump then
session.pump:resume();
end
end);