ATutor <= 2.2 (edit_marks.php) PHP Code Injection Vulnerability

• Software Link:

http://www.atutor.ca/

• Affected Versions:

Version 2.2 and prior versions.

• Vulnerability Description:

The vulnerable code is located in the /mods/_standard/gradebook/edit_marks.php script:

if (isset($_GET['asc'])) 
{
    $order = 'asc';
    $order_col = $addslashes($_GET['asc']);
} 
else if (isset($_GET['desc'])) {
    $order = 'desc';
    $order_col = $addslashes($_GET['desc']);

if ((isset($_GET["asc"]) || isset($_GET["desc"])) && $order_col <> "name")
{
    $sort = '$grades['.$order_col.'], SORT_'.strtoupper($order).', $selected_students, SORT_'.strtoupper($order);
    
    foreach($selected_tests as $test)
    {
        if ($test["gradebook_test_id"] <> $order_col)
            $sort .= ', $grades['.$test["gradebook_test_id"].'], SORT_'.strtoupper($order);
    }
    $sort='array_multisort('.$sort.');';
    eval($sort);
}

User input passed through the “asc” or “desc” GET parameters is not properly sanitized before being used in a call to the “eval()” function at line 195. This can be exploited to inject and execute arbitrary PHP code. Successful exploitation of this vulnerability should require an account with the “AT_PRIV_GRADEBOOK” privilege, however it could be exploited in conjunction with
KIS-2015-06 in order to bypass the authentication mechanism.

• Solution:

No official solution is currently available.

• Disclosure Timeline:

[06/10/2014] – Vendor notified
[09/10/2014] – Vendor response stating this issue has been added to the bug tracker and it is relatively minor
[13/10/2014] – Vendor replied saying he is not able to reproduce the issue and asked for further details
[29/10/2014] – Further exploitation details have been provided to the vendor
[11/11/2014] – Vendor replied saying he still is not able to reproduce the issue and asked for fix suggestions
[11/11/2014] – Some fix suggestions have been provided to the vendor
[30/09/2015] – CVE number requested
[05/10/2015] – CVE number assigned
[06/10/2015] – After one year still no official solution available
[04/11/2015] – Public disclosure

• CVE Reference:

The Common Vulnerabilities and Exposures project (cve.mitre.org)
has assigned the name CVE-2015-7712 to this vulnerability.

• Credits:

Vulnerability discovered by Egidio Romano.