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.

module:set_global();

local tostring = tostring;
local filters = require "util.filters";

local function log_send(t, session)
	if t and t ~= "" and t ~= " " then
		session.log("debug", "SEND: %s", tostring(t));
	end
	return t;
end

local function log_recv(t, session)
	if t and t ~= "" and t ~= " " then
		session.log("debug", "RECV: %s", tostring(t));
	end
	return t;
end

local function init_raw_logging(session)
	filters.add_filter(session, "stanzas/in",  log_recv, -10000);
	filters.add_filter(session, "stanzas/out", log_send,  10000);
end

filters.add_filter_hook(init_raw_logging);

function module.unload()
	filters.remove_filter_hook(init_raw_logging);
end