Oracle released the February 2013 Critical Patch Update for Java SE earlier than scheduled as an active exploitation of one of the vulnerabilities affecting the Java Runtime Environment (JRE) in desktop browsers has been widely reported.
The original Critical Patch Update for Java SE was scheduled on February 19th.
In addition to a number of security fixes, the February 2013 Critical Patch Update for Java SE contains fixes for 50 security vulnerabilities. 44 of these vulnerabilities only affect client deployment of Java (e.g., Java in Internet browsers). In other words, these vulnerabilities can only be exploited on desktops through Java Web Start applications or Java applets. In addition, one vulnerability affects the installation process of client deployment of Java (i.e. installation of the Java Runtime Environment on desktops).
3 of the vulnerabilities fixed in this Critical Patch Update apply to client and server deployment of Java; that means that these vulnerabilities can be exploited on desktops through Java Web Start and Java applets in Browser, or in servers, by supplying malicious input to APIs in the vulnerable server components. In some instances, the exploitation scenario of this kind of bugs on servers is very improbable; for example, one of these vulnerabilities can only be exploited against a server in the unlikely scenario that the server was allowed to process image files from an untrusted source.
Finally, 2 of the vulnerabilities fixed in this Critical Patch Update only apply to server deployment of the Java Secure Socket Extension (JSSE).
Furthermore, to help mitigate the threat of malicious applets (Java exploits in internet browsers), Oracle has switched the Java security settings to "high" by default. The "high" security setting requires users to expressly authorize the execution of unsigned applets allowing a browser user to deny execution of a suspicious applet (where in the past a suspicious applet could execute "silently"). As a result, unsuspecting users visiting malicious web sites will be notified before an applet is run and will gain the ability to deny the execution of the potentially malicious applet. In addition, Oracle has recently introduced the ability for users to disable Java in their browsers through the Java Control Panel on Windows.
For more information read the advisory for the February 2013 Critical Patch Update is located at http://www.oracle.com/technetwork/topics/security/javacpufeb2013-1841061.html