https://www.crowdstrike.com/blog/bears-midst-intrusion-democ...
The summary: One used Powershell modules and Windows Scheduler to run scripts. Another used a combination of Twitter and public sites like Github/Dropbox for command and control.
In my opinion, neither is impressively sophisticated, and a skilled application developer could whip up something similar in a week or two. Using popular sites like Twitter/Dropbox for C&C has been common for years, and you can purchase similar backdoors/RATs for less than $100.
edit: Another interesting point from the link above: the two exploits stole exactly the same info once inside the DNC network. This would obviously be a big no-no for a sophisticated state actor as it doubles your chance of being compromised, but the author explains it away by claiming that Russia's intelligence agencies are disorganized and adversarial.