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.

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#include <lua.h>

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#include <lauxlib.h>

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static int lc_xpcall (lua_State *L) {

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  int ret;

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  int n_arg = lua_gettop(L);

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  /* f, msgh, p1, p2... */

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  luaL_argcheck(L, n_arg >= 2, 2, "value expected");

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  lua_pushvalue(L, 1);  /* f to top */

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  lua_pushvalue(L, 2);  /* msgh to top */

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  lua_replace(L, 1); /* msgh to 1 */

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  lua_replace(L, 2); /* f to 2 */

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  /* msgh, f, p1, p2... */

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  ret = lua_pcall(L, n_arg - 2, LUA_MULTRET, 1);

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  lua_pushboolean(L, ret == 0);

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  lua_replace(L, 1);

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  return lua_gettop(L);

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}

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int luaopen_util_compat(lua_State *L) {

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	lua_createtable(L, 0, 2);

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	{

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		lua_pushcfunction(L, lc_xpcall);

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		lua_setfield(L, -2, "xpcall");

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	}

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	return 1;

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}