Backdoor and Vulnerabilities in Xerox

SEC Consult Security Advisory < 20100208-0 >

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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: www.xerox.com/information-security/enus.html

impact: critical

homepage: www.xerox.com

found: 2009-10-05

by: D. Fabian / SEC Consult / www.sec-consult.com

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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:

---------

www.xerox.com/information-security/enus.html

Advisory URL:

-------------

www.sec-consult.com/advisories_e.html

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EOF D. Fabian / @2009