Information
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Advisory by Netsparker.
Name: DOM XSS Vulnerability in Twenty Fifteen WordPress Theme
Affected Software : WordPress
Affected Versions: 4.2.1 and probably below
Vendor Homepage : https://wordpress.org/ and
https://wordpress.org/themes/twentyfifteen/
Vulnerability Type : DOM based Cross-site Scripting
Severity : Important
CVE-ID: CVE-2015-3429
Netsparker Advisory Reference : NS-15-007

Description
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By exploiting a Cross-site scripting vulnerability the attacker can
hijack a logged in user’s session. This means that the malicious
hacker can change the logged in user’s password and invalidate the
session of the victim while the hacker maintains access. As seen from
the XSS example in this article, if a web application is vulnerable to
cross-site scripting and the administrator’s session is hijacked, the
malicious hacker exploiting the vulnerability will have full admin
privileges on that web application.

Technical Details
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Proof of Concept URL for DOM XSS in WordPress:

http://example.com/wordpress/wp-content/themes/twentyfifteen/genericons/example.html#<img/src/onerror=alert(123)>

For more information on DOM based cross-site scripting vulnerabilities
read the following article:
https://www.netsparker.com/blog/web-security/dom-based-cross-site-scripting-vulnerability/

Advisory Timeline
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22/04/2015 - First Contact
07/05/2015 - Vulnerability fixed
07/05/2014 - Advisory released

Solution
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Download WordPress version 4.2.2 which includes fix for this vulnerability.

Credits & Authors
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These issues have been discovered by Omar Kurt while testing
Netsparker Web Application Security Scanner -
https://www.netsparker.com/web-vulnerability-scanner/

About Netsparker
--------------------
Netsparker finds and reports security issues and vulnerabilities such
as SQL Injection and Cross-site Scripting (XSS) in all websites and
web applications regardless of the platform and the technology they
are built on. Netsparker's unique detection and exploitation
techniques allows it to be dead accurate in reporting hence it's the
first and the only False Positive Free web application security
scanner. For more information visit our website on
https://www.netsparker.com