WebClientPrint Processor Unauthorized Proxy Modification

Type packetstorm
Reporter redteam-pentesting.de
Modified 2017-08-23T00:00:00


                                            `Advisory: WebClientPrint Processor 2.0: Unauthorised Proxy Modification  
RedTeam Pentesting discovered that attackers can configure a proxy host  
and port to be used when fetching print jobs with WebClientPrint  
Processor (WCPP). This proxy setting may be distributed via specially  
crafted websites and is set without any user interaction as soon as the  
website is accessed.  
Product: Neodynamic WebClientPrint Processor  
Affected Versions: (Microsoft Windows)  
Fixed Versions: >=  
Vulnerability Type: Man-in-the-Middle  
Security Risk: medium  
Vendor URL: http://www.neodynamic.com/  
Vendor Status: fixed version released  
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2015-010  
Advisory Status: published  
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH  
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  
"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  
in the URL bar of a browser opens the about box of WCPP.  
During RedTeam Pentesting's analysis of WCPP it was determined that WCPP  
ignores the system proxy configuration and by default tries to fetch  
print jobs directly, bypassing a proxy potentially configured in the  
system. WCPP can however be configured to use a (possibly different)  
proxy through "webclientprint" URLs. For example, visiting the following  
URL will set as a proxy IP for WCPP:  
Likewise, the port of the proxy can be changed to 14141 through this  
As soon as a proxy is initially configured, it will be used permanently  
without the need for any further confirmation. If a proxy was already  
configured before the URLs above are invoked, the old proxy will be  
replaced by the new one.  
Proof of Concept  
An attacker may prepare a malicious website with the following content:  
<iframe src="webclientprint:-proxyHost:">  
When visited by a WCPP user, the proxy host will be rewritten without any  
user interaction and without any visual indication.  
Likewise, the following HTML code may be used to define another proxy  
port when visited:  
<iframe src="webclientprint:-proxyPort:14141">  
This allows the proxy configuration to be changed without authorisation.  
Affected users should disable the WCPP handler and upgrade to a fixed  
version as soon as possible.  
Install a WCPP version greater or equal to[0].  
Security Risk  
If print jobs are fetched by WCPP over unencrypted HTTP, the  
unauthorised change of the proxy configuration may be exploited to yield  
a man-in-the-middle position. Attackers only need to trick users into  
visiting an attacker-controlled website which contains the configuration  
URLs as outlined above. Afterwards, all jobs printed via WCPP and  
fetched over HTTP will be requested through the proxy. This may lead to  
a disclosure of sensitive information depending on the printed  
documents. Furthermore, the integrity of the printed documents cannot be  
guaranteed anymore as attackers may also change the documents in  
If print jobs are fetched by WCPP over encrypted HTTPS, the unauthorised  
change of the proxy configuration results in a denial of service. After  
establishing a connection to the proxy, neither an HTTP request nor a  
TLS ClientHello is sent. The exact cause was not investigated any  
Overall, this vulnerability is rated as a medium risk. This estimation  
may need to be adapted depending on the protocol that is used to fetch  
print jobs.  
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  
[0] https://neodynamic.wordpress.com/2015/09/15/webclientprint-2-0-for-windows-clients-critical-update/  
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