Advisory ID: HTB23265
Product: qTranslate WordPress plugin
Vendor: Qian Qin 
Vulnerable Version(s): 2.5.39  and probably prior
Tested Version: 2.5.39 
Advisory Publication:  July 1, 2015  [without technical details]
Vendor Notification: July 1, 2015 
Public Disclosure: July 29, 2015 
Vulnerability Type: Cross-Site Scripting [CWE-79]
CVE Reference: CVE-2015-5535
Risk Level: Medium 
CVSSv2 Base Score: 4.3 (AV:N/AC:M/Au:N/C:N/I:P/A:N)
Discovered and Provided: High-Tech Bridge Security Research Lab ( https://www.htbridge.com/advisory/ ) 

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Advisory Details:

High-Tech Bridge Security Research Lab discovered vulnerability in qTranslate WordPress plugin, which can be exploited to perform Cross-Site Scripting (XSS) attacks against website administrators. Successful exploitation of this vulnerability may allow a remote attacker to gain complete control over the web application, if the victim visits a malicious page with XSS exploit. This vulnerability can also be used to perform drive-by-download or phishing attacks against website administrators. 

Input passed via "edit" HTTP GET parameter to "/wp-admin/options-general.php" is not properly sanitised before being returned to the user. A remote attacker can trick a logged-in administrator to open a specially crafted link and execute arbitrary HTML and script code in browser in context of the vulnerable website.

A simple exploit below will display a JS popup with "ImmuniWeb" word:

http://wordpress/wp-admin/options-general.php?page=qtranslate&edit=%22%3E%3Cscript%3Ealert%28%2FImmuniWeb%2F%29%3B%3C%2Fscript%3E


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Solution:

Disclosure timeline:
2015-07-01 Vendor notified via email, no reply.
2015-07-10 Vendor notified via emails and support thread on the WordPress plugin page, no reply.
2015-07-17 Vendor notified  via emails, no reply.
2015-07-28 Fix requested via emails, no reply.
2015-07-29 Public disclosure.

Currently we are not aware of any official solution from the vendor. As at temporary solution we strongly recommend disabling the vulnerable plugin. 

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References:

[1] High-Tech Bridge Advisory HTB23265 - https://www.htbridge.com/advisory/HTB23265 - Cross-Site Scripting (XSS) in qTranslate WordPress Plugin.
[2] qTranslate WordPress plugin - http://www.qianqin.de/ - qTranslate makes creation of multilingual content as easy as working with a single language.
[3] Common Vulnerabilities and Exposures (CVE) - http://cve.mitre.org/ - international in scope and free for public use, CVE® is a dictionary of publicly known information security vulnerabilities and exposures.
[4] Common Weakness Enumeration (CWE) - http://cwe.mitre.org - targeted to developers and security practitioners, CWE is a formal list of software weakness types.
[5] ImmuniWeb® SaaS - https://www.htbridge.com/immuniweb/ - hybrid of manual web application penetration test and cutting-edge vulnerability scanner available online via a Software-as-a-Service (SaaS) model.

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Disclaimer: The information provided in this Advisory is provided "as is" and without any warranty of any kind. Details of this Advisory may be updated in order to provide as accurate information as possible. The latest version of the Advisory is available on web page [1] in the References.