-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathredos-nodejs.html
247 lines (207 loc) · 11.2 KB
/
redos-nodejs.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="author" content="Thomas Loiret">
<meta name="description" content="When developing with NodeJS, you should be aware of regular expression denial of service (ReDoS).">
<meta name="fediverse:creator" content="@b0uh@mamot.fr">
<meta name="google-site-verification" content="jZBc2U9MHiBnSlgpoFEed-V3PZ16pMNv0GSX4hOh4mg" />
<title>ReDos + Node.js - Thomas Loiret - Random thoughts</title>
<!-- Custom styles for this template -->
<!-- build:css stylesheets/main.css -->
<link rel="stylesheet" href="https://b0uh.github.io/theme/css/main.min.css">
<link rel="stylesheet" href="https://b0uh.github.io/theme/css/custom.min.css">
<link rel="stylesheet" href="https://b0uh.github.io/theme/css/pygments/autumn.min.css">
<!-- endbuild -->
<link href="https://b0uh.github.io/feeds/all.atom.xml" type="application/atom+xml" rel="alternate" title="Thomas Loiret - Random thoughts Atom Feed" />
<!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries -->
<!--[if lt IE 9]>
<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
<script src="https://oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script>
<![endif]-->
<!-- Google Fonts -->
<script type="text/javascript">
WebFontConfig = {
google: { families: [ 'Open+Sans:300,400,700:latin', 'Lato:700,900:latin' ] }
};
(function() {
var wf = document.createElement('script');
wf.src = ('https:' == document.location.protocol ? 'https' : 'http') +
'://ajax.googleapis.com/ajax/libs/webfont/1/webfont.js';
wf.type = 'text/javascript';
wf.async = 'true';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(wf, s);
})();
</script>
</head>
<body>
<!-- header -->
<header class="header push-down-45">
<div class="container">
<!-- Brand and toggle get grouped for better mobile display -->
<div class="navbar-header">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#readable-navbar-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
</div>
<nav class="navbar navbar-default" role="navigation">
<!-- Collect the nav links, forms, and other content for toggling -->
<div class="collapse navbar-collapse" id="readable-navbar-collapse">
<ul class="navigation">
<li>
<a href="https://b0uh.github.io">Home</a>
</li>
<li>
<a href="https://b0uh.github.io/pages/about.html">About</a>
</li>
<li>
<a href="https://b0uh.github.io/pages/bookmarks.html">Bookmarks</a>
</li>
<li>
<a href="https://b0uh.github.io/archives.html">Archives</a>
</li>
</ul>
</div><!-- /.navbar-collapse -->
</nav>
<div class="hidden-xs hidden-sm">
<div class="social">
<a href="#" class="search__container">
<span class="glyphicon glyphicon-flash"></span>
</a>
<ul class="social__dropdown">
<li>
<a href="https://b0uh.github.io/feeds/all.atom.xml" target="_blank" class="social__container">
<span class="zocial-rss"></span>
</a>
</li>
<li>
<a href="https://mamot.fr/@b0uh" rel="me" target="_blank" class="social__container">
<img src="https://b0uh.github.io/theme/images/icons/mastodon-25px.png" />
</a>
</li>
<li>
<a href="https://www.linkedin.com/in/thomasloiret/" target="_blank" class="social__container">
<span class="zocial-linkedin"></span>
</a>
</li>
<li>
<a href="https://www.last.fm/user/b0uh" target="_blank" class="social__container">
<span class="zocial-lastfm"></span>
</a>
</li>
</ul>
</div>
</div>
</div>
</header>
<div class="container">
<div itemscope itemtype="http://schema.org/Article" class="boxed push-down-60">
<!-- Start of the blogpost -->
<div class="row">
<div class="col-xs-10 col-xs-offset-1 col-md-8 col-md-offset-2 push-down-60">
<!-- Start of the content -->
<div class="post-content">
<h1 itemprop="name">ReDos + Node.js</h1>
<div class="meta__container--without-image">
<div class="row">
<div class="col-xs-12 col-sm-8">
<span itemprop="author" itemscope itemtype="http://schema.org/Person">
<div class="meta__info" itemprop="name">
Thomas Loiret
</div>
</span>
</div>
<div class="col-xs-12 col-sm-4">
<div class="meta__comments">
<span class="meta__date" itemprop="datePublished" content="2019-11-27">
<span class="glyphicon glyphicon-calendar"></span> Wed 27 November 2019
</span>
</div>
</div>
</div>
</div>
<span itemprop="articleBody">
<p><strong>TL;DR:</strong> When developing with NodeJS, you should be aware of regular expression denial of service (ReDoS).</p>
<h2>Introduction</h2>
<p>A ReDoS (Regular expression Denial of Service) is a type of attack used to put down a web server. This is possible when the code run by the server contains a regular expression that triggers too many backtracking.</p>
<p>Let's step back quickly to understand what it really means when developing with Node.js. It is important to understand how the event loop works. It <a href="https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/">"allows Node.js to perform non-blocking I/O operations — despite the fact that JavaScript is single-threaded — by offloading operations to the system kernel whenever possible"</a>. Therefore we should avoid to <a href="https://nodejs.org/en/docs/guides/dont-block-the-event-loop/">block the event loop</a>.</p>
<p>When the event loop is blocked Node.js cannot process anything else and the server is paralyzed. When the code contains unsafe regular expressions it can become an attack vector. Instead of having to send a lot of requests to put down a server with a classic DoS, you can send only a few requests that will trigger the unsafe regular expression and put down the server.</p>
<h2>Examples</h2>
<p>Try to execute the following regular expression with the suggested input. You will notice that Node.js take a long time (several seconds) to respond.</p>
<div class="highlight"><pre><span></span><code><span class="sr">/^(A+)*B/</span><span class="p">.</span><span class="nx">test</span><span class="p">(</span><span class="s1">'A'</span><span class="p">.</span><span class="nx">repeat</span><span class="p">(</span><span class="mf">30</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s1">'E'</span><span class="p">)</span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="sr">/(\w+\d+)+C/</span><span class="p">.</span><span class="nx">test</span><span class="p">(</span><span class="s1">'a1'</span><span class="p">.</span><span class="nx">repeat</span><span class="p">(</span><span class="mf">25</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s1">','</span><span class="p">)</span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="sr">/\s*\n/</span><span class="p">.</span><span class="nx">test</span><span class="p">(</span><span class="s1">' '</span><span class="p">.</span><span class="nx">repeat</span><span class="p">(</span><span class="mf">50000</span><span class="p">))</span>
</code></pre></div>
<h2>What can I do about it?</h2>
<p>There are some tools out there like <a href="https://github.com/substack/safe-regex"><code>safe-regex</code></a> and <a href="https://www.cs.bham.ac.uk/~hxt/research/rxxr2/"><code>rxxr2</code></a> to try to detect unsafe regular expressions. Unfortunately none of them work 100% of the time.</p>
<p>Since this security issue is directly linked to how Node.js interprets regular expression, the safest solution is to use a different engine: <a href="https://github.com/google/re2/"><code>re2</code></a>. However, switching engine also means that some of your regular expressions may <a href="https://www.npmjs.com/package/re2#limitations-things-re2-does-not-support">not work anymore</a>.</p>
<p>In conclusion, you can continue to use Node.js regular expression engine as long as you as aware of ReDoS and avoid catastrophic backtracking. If you are not sure about your code, don't hesitate to use <code>re2</code>, this is the simplest solution to be safe :)</p>
</span>
<div class="meta__container--without-image">
<div class="row">
</div>
</div>
<br>
</div>
</div>
</div>
</div>
</div>
<footer class="copyrights">
<div class="container">
<div class="row">
<div class="col-xs-12 col-sm-6">
Powered by <a href="https://github.com/getpelican/pelican">Pelican</a>.
</div>
<div class="col-xs-12 col-sm-6">
<div class="copyrights--right">
Made with <span class="glyphicon glyphicon-heart"></span> in Nantes.
</div>
</div>
</div>
</div>
</footer>
<script src="https://b0uh.github.io/theme/scripts/jquery.min.js"></script>
<script src="https://b0uh.github.io/theme/scripts/underscore.min.js"></script>
<script src="https://b0uh.github.io/theme/scripts/bootstrap.min.js"></script>
<script src="https://b0uh.github.io/theme/scripts/main.min.js"></script>
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-98369697-1', 'auto');
ga('send', 'pageview');
</script>
<!-- Chiffre.io - Privacy-first analytics -->
<script id="chiffre:analytics-config" type="application/json">
{
"publicKey": "pk.VvetZOQ0g5XwOL2W6hVvG7gFQTk3xdUMczDkqSCZUxE",
"pushURL": "https://push.chiffre.io/event/ceJKfYgcLN6XkYn8"
}
</script>
<script
src="https://embed.chiffre.io/analytics.js"
crossorigin="anonymous"
async=""
>
</script>
<noscript>
<img
src="https://push.chiffre.io/noscript/ceJKfYgcLN6XkYn8"
alt="Chiffre.io anonymous visit counting for clients without JavaScript"
crossorigin="anonymous"
width="1px"
height="1px"
style="display:none"
/>
</noscript>
</body>
</html>