"the code delivers Remote Access Tools (RATs) and evades detection using a range of techniques."
A "range of techniques" includes things like rootkits.
>No rootkits,
The attackers did use stealthy persistence techniques often called 'rootkits".
"the SeaDaddy implant developed in Python and compiled with py2exe and another Powershell backdoor with persistence accomplished via Windows Management Instrumentation (WMI) system,[..] The Powershell backdoor is ingenious in its simplicity and power" [0]
>no 0 days
The same group used six 0-days in 2015. Either they didn't need to use them in this attack or they used them and deleted the evidence. Senit is APT28 see quote below:
"One of the striking characteristics of the Sednit group is its ability to come up with brand-new 0-day vulnerabilities regularly. In 2015, the group exploited no fewer than six 0-day vulnerabilities" [1]
>yet it was the most routine, simple attack conceivable.
The attack involved multiple pieces of custom written software and carefully researched spearfishing, the attackers spent time and effort to hide their tracks, maintain persistence and exfil data without detection. This level of effort and time does not qualify as routine, some intelligence agencies can't even write their own RATs.
[0]: https://www.crowdstrike.com/blog/bears-midst-intrusion-democ...
[1]: http://www.welivesecurity.com/wp-content/uploads/2016/10/ese...