SEC Consult Security Advisory < 20100208-0 >

          title: Backdoor and Vulnerabilities in Xerox 
                 WorkCentre Printers Web Interface
       products: Xerox WorkCentre 5665/5675/5687

vulnerable version: 21.120.39.000 and possibly others
fixed version: http://www.xerox.com/information-security/enus.html
impact: critical
homepage: http://www.xerox.com/
found: 2009-10-05
by: D. Fabian / SEC Consult / www.sec-consult.com

Vendor description:

WorkCentre 5665 / 5675 / 5687
High-speed performance, outstanding productivity and advanced
multifunction capabilities. These are the essentials of the all-in-one
offce powerhouse that easily handles the high-volume print demands of
large, busy workgroups. And with robust copying, scanning, faxing and a
host of innovative Xerox technologies, you get a total workfow solution
that excels at streamlining your unique job processes.

Vulnerability 1: Backdoor to Mailboxes

For some reasons, Xerox decided to integrate a backdoor into the scan
system of the WorkCentre 5665 / 5675 / 5678 web interface. Scan folders
("mailboxes") can be protected with a password. The documentation says
on folder passwords:

"A folder password may or may not be required depending on the Scan
Policies set by the administrator. If a password is required to create
a folder, type the password here. If no password is required by the
Scan Policies, you can optionally choose whether or not to password
protect your folder."

Some files require a job password. If someone tries to access a private
folder without logging in previously, this does not work since a cookie
is compared to a precomputed checksum. However there is a script named
"YoUgoT_It.php" that creates the correct checksum for any folder. By
simply calling the script with the folder name as argument, an attacker
can access any folder.

Here is the relevant code from the file folder.php that allows access,
if the checksum is correct:

    /* see if the private folder is trying to be accessed, without
    logging in previously; this can be done by checking to see if
    the cookie matches the computed "checksum" */
    
    if ( $gFolderName === $_SESSION['MBOX_FOLDER'] )
    {
            // continue on as this is okay
    }
    elseif (( false === isset( $_COOKIE[$gFolderName] )) ||
            ( $theChecksum !== $_COOKIE[$gFolderName] ))
    {
            header( "Location: /mailbox/pin.php?" . NAME_KEY .
    "=" . $gFolderName ); exit;
    }

Vulnerability 2: Authentication not validated

In multiple instances, when a password is required to access certain
pages, the developers seemed to forget the vital "die()" or "exit()"
statement after the redirect. This allows an attacker access to
multiple pages that would require authentication.

Here are a couple of examples:
/diagnostics/authenticationQuery.php:

    if ( "" === $gUserName )
    {
            header( "Location: /properties/authentication/login.php?redir=" .
                                    $_SERVER['SCRIPT_NAME'] );
    }
    elseif ( false === $gSaLoggedIn )
    {
            header( "Location: /properties/no_modify.php" );
    }

/php_includes/sa_check.php: This script seems to check whether the
currently logged in user is an administrative user

    if ( "" === $gUserName )
    {
            header( "Location: /properties/authentication/login.php?redir=" .
                                    $_SERVER['REQUEST_URI'] );
    }
    elseif (( false === $gSaLoggedIn ) &&
                    ( "" !== $gUserName ))
    {
            header( "Location: /properties/no_modify.php" );
            exit;
    }

As you can see from the code, if the user is logged in, but not an
administrator, he is correctly denied access. However if the
user is not logged in at all, only a Location-header is sent,
but the rest of the script can continue to run.

The very same vulnerability can be found in many cases. In some cases,
the authentication is also only in the page that provides only the
frameset. The actual content-pages can be called without any
authentication at all.

Vulnerable versions:

The vulnerabilities were discovered in version 21.120.39.000. It is
likely that other versions are affected also.

Vendor contact timeline:

2009-10-06: Contacting the Xerox Security Team via Email

Solution:

http://www.xerox.com/information-security/enus.html
http://www.xerox.com/downloads/usa/en/c/cert_XRX10-002_v1.0.pdf

Advisory URL:

https://www.sec-consult.com/advisories_e.html#a65

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EOF D. Fabian / @2009