ExpressionEngine 2.5.1 was quietly released last night. There’s a small security fix, a large number of bug fixes, a handy change to Template::parse_variables() for our third party developers, and—most importantly—support for IPv6 IP addresses.
On June 6th, 2012, major ISPs and networking equipment manufacturers are permanently enabling IPv6 for their products and services. ExpressionEngine previously did not support these IPv6 IP addresses which meant your users might not be able to log in, comment, or fill out forms. As of the 2.5.1 update, IPv6 IP addresses are supported and your visitors can continue to use your sites unaffected.
Also, 2.5.1 is the last release that will support PHP 5.1.6 and MySQL 4.1. With the next major release—2.6—we will require PHP 5.2.4 and MySQL 5.0.3.
The changelog is up in it’s normal place and has all of the changes in detail.