Talos has investigated a targeted malware campaign against South Korean users. The campaign was active between November 2016 and January 2017, targeting a limited number of people. The infection vector is a Hangul Word Processor document (HWP), a popular alternative to Microsoft Office for South Korean users developed by Hancom.
The malicious document in question is written in Korean with the following title:
|5170101-17년_북한_신년사_분석.hwp (translation: 5170101-17 __ North Korea _ New Year _ analysis .hwp)|
An interesting twist also came within the analysed malicious document as it attempts to download a file from an official Korean government website: kgls.or.kr (Korean Government Legal Service). The file downloaded is a binary masquerading as a jpeg file that is later executed as part of the infection. It's likely that the website was compromised by the attackers to try and legitimise the HTTP GET attempts for the final payload, this traffic would potentially not have looked unfamiliar for any system administrators.
The attackers' infrastructure appeared to be up for a few days at a time with no observed infrastructure re-use occurring. Unfortunately, the compromised sites were all either cleaned or removed by the attackers and Talos were unable to obtain the final payload. This level of operational security is common for sophisticated attackers.
Due to these elements it's likely that this loader has been designed by a well-funded group in order to target public sector entities in South Korea. Many of these techniques fit the profile of campaigns previously associated with attacks by certain government groups.