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<h1>Script Injection Attacks</h1>
<p class="para">
If you are using JavaScript, make sure that any variables that cross the PHP-
to-JavaScript boundry are passed in the <em>scope</em> field of
<a href="class.mongodb-bson-javascript.html" class="classname">MongoDB\BSON\Javascript</a>, not interpolated into the
JavaScript string. This can come up when using <em>$where</em>
clauses in queries, mapReduce and group commands, and any other time you may
pass JavaScript into the database.
</p>
<p class="para">
For example, suppose we have some JavaScript to greet a user in the database
logs. We could do:
</p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// Don't do this!!!<br /></span><span style="color: #0000BB">$username </span><span style="color: #007700">= </span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'field'</span><span style="color: #007700">]; <br /><br /></span><span style="color: #0000BB">$cmd </span><span style="color: #007700">= new \</span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Command</span><span style="color: #007700">( [<br /> </span><span style="color: #DD0000">'eval' </span><span style="color: #007700">=> </span><span style="color: #DD0000">"print('Hello, </span><span style="color: #0000BB">$username</span><span style="color: #DD0000">!');"<br /></span><span style="color: #007700">] );<br /><br /></span><span style="color: #0000BB">$r </span><span style="color: #007700">= </span><span style="color: #0000BB">$m</span><span style="color: #007700">-></span><span style="color: #0000BB">executeCommand</span><span style="color: #007700">( </span><span style="color: #DD0000">'dramio'</span><span style="color: #007700">, </span><span style="color: #0000BB">$cmd </span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<p class="para">
However, what if a malicious user passes in some JavaScript?
</p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// Don't do this!!!<br /></span><span style="color: #0000BB">$username </span><span style="color: #007700">= </span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'field'</span><span style="color: #007700">]; <br /></span><span style="color: #FF8000">// $username is set to "'); db.users.drop(); print('"<br /><br /></span><span style="color: #0000BB">$cmd </span><span style="color: #007700">= new \</span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Command</span><span style="color: #007700">( [<br /> </span><span style="color: #DD0000">'eval' </span><span style="color: #007700">=> </span><span style="color: #DD0000">"print('Hello, </span><span style="color: #0000BB">$username</span><span style="color: #DD0000">!');"<br /></span><span style="color: #007700">] );<br /><br /></span><span style="color: #0000BB">$r </span><span style="color: #007700">= </span><span style="color: #0000BB">$m</span><span style="color: #007700">-></span><span style="color: #0000BB">executeCommand</span><span style="color: #007700">( </span><span style="color: #DD0000">'dramio'</span><span style="color: #007700">, </span><span style="color: #0000BB">$cmd </span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<p class="para">
Now MongoDB executes the JavaScript string
<em>"print('Hello, '); db.users.drop(); print('!');"</em>.
This attack is easy to avoid: use <em>args</em> to pass
variables from PHP to JavaScript:
</p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'field'</span><span style="color: #007700">] = </span><span style="color: #DD0000">'derick'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$args </span><span style="color: #007700">= [ </span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'field'</span><span style="color: #007700">] ];<br /><br /></span><span style="color: #0000BB">$cmd </span><span style="color: #007700">= new \</span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Command</span><span style="color: #007700">( [<br /> </span><span style="color: #DD0000">'eval' </span><span style="color: #007700">=> </span><span style="color: #DD0000">"function greet(username) { print('Hello, ' + username + '!'); }"</span><span style="color: #007700">,<br /> </span><span style="color: #DD0000">'args' </span><span style="color: #007700">=> </span><span style="color: #0000BB">$args</span><span style="color: #007700">,<br />] );<br /><br /></span><span style="color: #0000BB">$r </span><span style="color: #007700">= </span><span style="color: #0000BB">$m</span><span style="color: #007700">-></span><span style="color: #0000BB">executeCommand</span><span style="color: #007700">( </span><span style="color: #DD0000">'dramio'</span><span style="color: #007700">, </span><span style="color: #0000BB">$cmd </span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<p class="para">
This adds an argument to the JavaScript scope, which gets used as argument
for the <em>greet</em> function. Now if
someone tries to send malicious code, MongoDB will harmlessly print
<em>Hello, '); db.dropDatabase(); print('!</em>.
</p>
<p class="para">
Using arguments helps to prevent malicious input from being executed by the
database. However, you must make sure that your code does not turn around
and execute the input anyway! It is best to avoid executing
<em class="emphasis">any</em> JavaScript on the server in the first place.
</p>
<p class="para">
You are strongly recommended to stay clear of the <a href="https://docs.mongodb.com/manual/reference/operator/query/where/#considerations" class="link external">» $where
clause</a> with queries, as it impacts performance significantly. Where
possible, use either normal query operators, or the <a href="https://docs.mongodb.com/manual/core/aggregation-pipeline" class="link external">» Aggregation
Framework</a>.
</p>
<p class="para">
As alternative to <a href="https://docs.mongodb.com/manual/core/map-reduce/" class="link external">» MapReduce</a>, which uses
JavaScript, consider using the <a href="https://docs.mongodb.com/manual/core/aggregation-pipeline" class="link external">» Aggregation
Framework</a>. Unlike Map/Reduce, it uses an idiomatic language to
construct queries, without having to write, and use, the slower JavaScript
approach that Map/Reduce requires.
</p>
<p class="para">
The <a href="https://docs.mongodb.com/manual/reference/command/eval/" class="link external">» eval command</a>
has been deprecated since MongoDB 3.0, and should also be avoided.
</p>
</div>
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