prosody
783056b4e448
util/xml.lua

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Software / code / prosody

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util/xml.lua @ 12181:783056b4e448 0.11 0.11.12

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.
author Jonas Schäfer <jonas@wielicki.name>
date Mon, 10 Jan 2022 18:23:54 +0100
parent 8555:4f0f5b49bb03
child 12201:e5e0ab93d7f4
comparison
equal deleted inserted replaced
12090:e77735354fad 12181:783056b4e448
1 1
2 local st = require "util.stanza"; 2 local st = require "util.stanza";
3 local lxp = require "lxp"; 3 local lxp = require "lxp";
4 local t_insert = table.insert; 4 local t_insert = table.insert;
5 local t_remove = table.remove; 5 local t_remove = table.remove;
6 local error = error;
6 7
7 local _ENV = nil; 8 local _ENV = nil;
8 -- luacheck: std none 9 -- luacheck: std none
9 10
10 local parse_xml = (function() 11 local parse_xml = (function()
11 local ns_prefixes = { 12 local ns_prefixes = {
12 ["http://www.w3.org/XML/1998/namespace"] = "xml"; 13 ["http://www.w3.org/XML/1998/namespace"] = "xml";
13 }; 14 };
14 local ns_separator = "\1"; 15 local ns_separator = "\1";
15 local ns_pattern = "^([^"..ns_separator.."]*)"..ns_separator.."?(.*)$"; 16 local ns_pattern = "^([^"..ns_separator.."]*)"..ns_separator.."?(.*)$";
16 return function(xml) 17 return function(xml, options)
17 --luacheck: ignore 212/self 18 --luacheck: ignore 212/self
18 local handler = {}; 19 local handler = {};
19 local stanza = st.stanza("root"); 20 local stanza = st.stanza("root");
20 local namespaces = {}; 21 local namespaces = {};
21 local prefixes = {}; 22 local prefixes = {};
62 stanza:text(data); 63 stanza:text(data);
63 end 64 end
64 function handler:EndElement() 65 function handler:EndElement()
65 stanza:up(); 66 stanza:up();
66 end 67 end
67 local parser = lxp.new(handler, "\1"); 68 local parser;
69 -- SECURITY: These two handlers, especially the Doctype one, are required to prevent exploits such as Billion Laughs.
70 function handler:StartDoctypeDecl()
71 if not parser.stop or not parser:stop() then
72 error("Failed to abort parsing");
73 end
74 end
75 function handler:ProcessingInstruction()
76 if not parser.stop or not parser:stop() then
77 error("Failed to abort parsing");
78 end
79 end
80 if not options or not options.allow_comments then
81 -- NOTE: comments are generally harmless and can be useful when parsing configuration files or other data, even user-provided data
82 function handler:Comment()
83 if not parser.stop or not parser:stop() then
84 error("Failed to abort parsing");
85 end
86 end
87 end
88 parser = lxp.new(handler, ns_separator);
68 local ok, err, line, col = parser:parse(xml); 89 local ok, err, line, col = parser:parse(xml);
69 if ok then ok, err, line, col = parser:parse(); end 90 if ok then ok, err, line, col = parser:parse(); end
70 --parser:close(); 91 --parser:close();
71 if ok then 92 if ok then
72 return stanza.tags[1]; 93 return stanza.tags[1];