PlugX Malware Found in Official Releases of League of Legends, Path of Exile

Hacks in Taiwan (HITCON), a security conference hosted in that country, has discovered an attack involving several online games. Official releases of two popular online games were found to be compromised, downloading malware onto computers. HITCON worked with Trend Micro to provide a clean-up tool to possible victims of the attack. Trend Micro was then able to coordinate with the affected game provider to help address the incident.

Compromised Official Releases

The games that were used in the attack were online games League of Legends (LoL) and Path of Exile (PoE). Variants of the remote access Trojan (RAT) PlugX were found in the official releases of the three games, and appeared to target users based in certain countries in Asia.

The infection chain is triggered by downloading the legitimate installer or updates for the game itself. The compromised game launcher will then drop three files:

A legitimate game launcher
A “cleaner” that overwrites the compromised launcher with the legitimate one
A dropper installs PlugX binaries

The cleaner file could be seen as one way of covering up any traces of malicious activity. In the end, the victim will only see two malicious files, NtUserEx.dll and NtUserEx.dat (both detected as BKDR_PLUGX.ZTBL-EC).

PlugX allows remote users to perform malicious and data theft routines on a system without the user’s permission or authorization. PlugX variants often target legitimate apps so the use of these games is not new. One marked difference is that this PlugX variant created its own autostart service rather than relying on the legitimate app’s.

A closer look reveals that the string “Cooper” can be found in the malware’s body. In a separate APT campaign the name “Lee Cooper” was used as the registrant of the C&C server, which may indicate that the same attacker group is responsible for this campaign as well.

Figure 1. The string “Cooper” can be found in the malware

While checking the certificate, we noticed that the hash value applied to the suspect file was VALID, which means that the “signing tool” was used to pair with the compromised binary’s hash. The clean game launcher, on the other hand, has an invalid digital signature.

Tracing the Source

These compromised official releases were traced back to Garena, a consumer Internet platform provider in Asia. Garena has partnerships with game developers such as Riot Games, S2 Games, and Electronic Arts, allowing the company to have exclusive releases to certain games.

In an official post, Garena stated that “computers and patch servers were infected with Trojans. As a result, all the installation files distributed for the games League of Legends and Path of Exile are infected.”

Taiwan and Singapore, Most Affected

Based on analysis, it seems that only the Taiwanese versions of the LoL and PoE installers were compromised. Feedback from the Trend Micro™ Smart Protection Network™ supports these findings. However, we have also seen victims from other Asian countries such as Thailand, Malaysia, and Hong Kong.

Figure 3. Affected countries

Analysis of the C&C activity shows that these countries are part of the top countries which accessed the C&C server. Activity for the malware died down soon after Garena released their official announcement.

Protecting the Gamers

Currently, the installers on Garena’s website and other associated links have been verified to be clean since December 29, 2014. Trend Micro has released a clean-up tool for related infections that gamers may use. Garena has also recommended several steps to protecting player accounts: