According to the experts at Cisco Talos, the cyber espionage campaign was active between November 2016 and January 2017 and leveraged on vulnerabilities in a Korean language word processing program (Hangul Word Processor document (HWP)) and a spoofed document from the Korean Ministry of Unification.
The cyber espionage campaign was conducted simultaneously ballistic missile tests conducted by North Korea in early February and shortly before the announced a joint military exercise organized by the United States and South Korea.
Malware researchers who investigated the cyber attacks discovered that the threat actors used a compromised Korean government website (kgls.or.kr (Korean Government Legal Service)) to download secondary payloads onto compromised machines.
The file downloaded is a binary masquerading as a jpeg image file that is then executed as part of the infection.
The experts noticed that the hackers used a proprietary format of the Hangul Word Processor, which is a local word processor, a circumstance that suggests the involvement of well-funded group interested in hacking South Korean targets, especially Government offices.
Hackers used a bait document titled “Analysis of “Northern New Year” in 2017,” it includes a logo of the Ministry Of Unification at the bottom of the document.
“This is a fairly unusual choice as this software is rarely used outside of Korea, but it is known to be widely used within Korea, including use by the South Korean government. As a regional file format, many security devices are not equipped to process HWP files. This can allow an attacker a vector with a much lower risk of detection by any security scanning devices.” reads the analysis shared by the Talos Group.
The documents were used to drop malware files with different hash but with the same purpose:
The experts at Talos were able to the Command and Control infrastructure used by the hackers, four servers that were based in the following countries:
Investigators believe the attack was backed by North Korea, the TTPs (Techniques, tactics, and procedures) match the profile of campaigns previously associated with nation-state actors. North Korea is the main suspect, but in the past also the US NSA compromised computer networks in South Korea, primarily to spy on the government of Pyongyang.
North Korea has launched numerous cyber attacks against the South across the years, the Dark Seoul is probably one of the most popular hacking campaigns that targeted banks and broadcasters in 2013.
In the past other attacks leveraged on flaws in the Hangul Word Processor, in September 2015 security experts from FireEye speculated that the North Korea carried out the cyber attacks against the South Korea by exploiting a zero-day ( CVE-2015-6585) in the word processing program widely used in that country.
According to a report published by FireEye, the Hangul Word Processor is a proprietary software primarily used by government and public institutions in the South Korea, for this reason, the North Korea allegedly exploited it the attack vector.
Back to the present, let me suggest to read the report, it also includes IoCs.
(Security Affairs – North Korea, Information Warfare, South Korea)