Yesterday VMware released security and bugfix patches for both ESXi 5.0 and ESXi 5.1. It has also updated the vCenter Server Appliance to address security issues as well. For the full security bulletin, check out this link. The new build numbers are shown below:
ESXi 5.0 Build 914586 (Update 2)
ESXi 5.1 Build 914609
As always, you can download the patches from their patch manager site here.