RTE open in new window not Working

There is a XSS Filter known issue with the RTE component affecting Adobe CQ 5.6, the XSS filter trims the target attribute of the a element.

Symptom
Inside the RTE component, the open in new window feature of the hyperlink component doesn’t work. As a result, the link is opened in the same page.

Solution
We need to declare the target attribute in the antisamy configuration file in CRXDE Light as follow:

1. Copy /libs/cq/xssprotection/config.xml to /apps/cq/xssprotection/config.xml.
2. Open /apps/cq/xssprotection/config.xml.
3. In the common-attributes section, add the following target attribute declaration.

<attribute name="target">
    <regexp-list>
        <regexp value="[a-zA-Z0-9-_\$]+"/>
    </regexp-list>
</attribute>

1. Find the tag declaration by searching the term
2. Add the line below in the list of attributes.

<attribute name="target" />

Save the file.
http://helpx.adobe.com/experience-manager/kb/target-attribut-issue-tag.html