Security researchers at Intezer and McAfee have conducted a joint investigation that allowed them to collect evidence that links malware families attributed to North Korean APT groups such as the notorious Lazarus Group and Group 123.

The experts focused their analysis on the code reuse, past investigations revealed that some APT groups share portions of code and command and control infrastructure for their malware.

Security researchers when analyzing a hacking campaign attempt to attribute it to a specific threat actor also evaluating the code reuse.

“The following graph presents a high-level overview of these relations. Each node represents a malware family or a hacking tool (“Brambul,” “Fallchill,” etc.) and each line presents a code similarity between two families. A thicker line correlates to a stronger similarity. In defining similarities, we take into account only unique code connections, and disregard common code or libraries. This definition holds both for this graph and our entire research.” reads the analysis published by the experts.

“We can easily see a significant amount of code similarities between almost every one of the attacks associated with North Korea. Our research included thousands of samples, mostly unclassified or uncategorized.”

According to the experts, North Korea-linked groups operated with two main goals, raise money and pursue nationalist aims.

Each state-sponsored hacker was involved in cyber operations with one of the above goals depending on his cyber capabilities.

Financially motivated operations consisting in hacking into financial institutions, hijack gambling sessions or sell pirated and cracked software were conducted by the Unit 180. Operations with nationalist aims are mostly executed by the Unit 121.

The joint research conducted by the experts was focused on the larger-scale nationalism-motivated campaigns, most of which presented a significant code reuse.

The experts analyzed thousands of malware samples, many still unclassified or uncategorized, and discovered many similarities in the source code used in attacks associated with North Korea.

For example, the “Common SMB module” that was part of the WannaCry Ransomware (2017) was similar to the code used the malware Mydoom (2009), Joanap, and DeltaAlfa.

“The first code example appeared in the server message block (SMB) module of WannaCry in 2017, Mydoom in 2009, Joanap, and DeltaAlfa. Further shared code across these families is an AES library from CodeProject. These attacks have been attributed to Lazarus; that means the group has reused code from at least 2009 to 2017.” states the analysis published by the experts.

The expert notices many similarities in the source code of three different remote access Trojans, tracked as NavRAT, Gold Dragon, and a DLL that was used in the attack against the South Korean gambling industry. The similarity consists in the Common file mapping.

“The second example demonstrates code responsible for mapping a file and using the XOR key 0xDEADBEEF on the first four bytes of the file. This code has appeared in the malware families NavRAT and Gold Dragon, plus a certain DLL from the South Korean gambling hacking campaign.” reads the report published by the experts.

The three malware were associated with the APT group tracked as Group 123 (also tracked as Reaper, APT37, and ScarCruft).

The researchers also found a similarity in the source code of the Brambul malware (2009) and KorDllBot (2011).

“The third example, responsible for launching a cmd.exe with a net share, has been seen in 2009’s Brambul, also known as SierraBravo, as well as KorDllBot in 2011. These malware families are also attributed to the Lazarus group.” states the report.

The experts also discovered a connection between the Tapaoux (or DarkHotel) malware family and samples involved in the Operation Troy.

The analysis of the code reuse conducted by the experts confirmed that most of the samples attributed to North Korea-linked APT group Lazarus presented many similarities. The only malware that appears different are the RATs involved in the operations attributed to Group 123 APT group.

“The malware attributed to the group Lazarus has code connections that link many of the malware families spotted over the years. Lazarus is a collective name for many DPRK cyber operations, and we clearly see links between malware families used in different campaigns,” the researchers concluded.

“We clearly saw a lot of code reuse over the many years of cyber campaigns we examined. This indicates the North Koreans have groups with different skills and tools that execute their focused parts of cyber operations while also working in parallel when large campaigns require a mix of skills and tools.” concluded the experts.

Pierluigi Paganini

( Security Affairs – North Korea, malware)

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