Apple has recently announced that new and updated apps submitted to the Apple App Store must include 64-bit support for them to be approved. This change will be implemented by the Apple App Store starting February 1, 2015.
This means that starting at that time, Cordova-based apps should be built using a version of Cordova that has 64-bit iOS support.
The first version of Cordova to include 64-bit for iOS is 3.4.1. Therefore, to meet these requirements of the Apple App Store, you should be using at least version 3.4.1 of Cordova before this February deadline.
The 64-bit support for iOS is in the form of a fat binary that contains 32-bit and 64-bit code. This form of fat binary is only supported for iOS 5.1.1 and up. So when creating iOS apps with 64-bit support, you will not be able to target them for iOS versions earlier than 5.1.1.
If you are on a version of Cordova older than 3.4.1 and building iOS apps, you are encouraged to upgrade to a more recent version before Apple's deadline. For upgrade instructions, please see the Updating Cordova and Your Project section of the documentation. You may also find upgrade hints in the blog, such as this recent one for iOS 3.7.0. The Apache community has no plans to backport the iOS 64-bit capability to earlier versions of Cordova.
Additionally, if your iOS project already exists and was originally created before 3.4.1, you will need to update the Build Settings for Architectures and Valid Architectures as described in this issue.
You need to also meet the rest of the requirements outlined in Apple's announcement, including using Xcode 6 and the iOS 8 SDK.