Originally Posted by Chris Boulton

MyBB 1.2.1 is now available on the MyBB site and is a security update & bug fix maintenance release.

We've fixed several issues identified in MyBB 1.2 in this release and added support for Internet Explorer's HttpOnly cookies. There have also been some publicly disclosed security related issues (minor severity) identified with 1.2 and a more potentially high risk vulnerability which was not transitioned from 1.1.8 to 1.2 which are all fixed in this release.

We recommend that all users upgrade to 1.2.1 so their board is patched against these vulnerabilities and running a more stable copy of the MyBB 1.2 series.

Information on upgrading, template changes and language changes can be found in the posts below.

If for some reason you cannot immediately update to this release:
We recommend applying the attached manual patch instructions for the moderately-high risk vulnerability identified in MyBB 1.2. You should only consider this a temporary solution and make the effort to upgrade to 1.2.1.