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) 2008-2017 Matthew Wild
-- Copyright (C) 2008-2017 Waqas Hussain
-- Copyright (C) 2008-2017 Kim Alvefur
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
local s_gsub = string.gsub;
local random_bytes = require "util.random".bytes;
local base64_encode = require "util.encodings".base64.encode;
local b64url = { ["+"] = "-", ["/"] = "_", ["="] = "" };
local function b64url_random(len)
return (s_gsub(base64_encode(random_bytes(len)), "[+/=]", b64url));
end
return {
short = function () return b64url_random(6); end;
medium = function () return b64url_random(12); end;
long = function () return b64url_random(24); end;
custom = function (size)
return function () return b64url_random(size); end;
end;
}