source: https://www.securityfocus.com/bid/48951/info

Skype is prone to an HTML-injection vulnerability because it fails to properly sanitize user-supplied input before using it in dynamically generated content.

Successful exploits will allow attacker-supplied HTML and script code to run in the context of the affected browser, potentially allowing the attacker to steal cookie-based authentication credentials or to control how the site is rendered to the user. Other attacks are also possible.

Skype 5.3.0.120 and prior are vulnerable; other versions may also be affected.

The following sample input is available:

"><iframe src='' onload=alert('mphone')>

A video demonstrating the attack is available. Please see the references for more information.