Symantec Discovers Strider, A New CyberEspionage Group

Symantec has discovered a previously unknown cyberespionage group so selective in its targets that it is only known to have compromised seven organizations and 36 endpoints since it started operating five years ago. Dubbed "Strider" by Symantec, the threat actor's malware of choice is a custom, Windows infostealer called Remsec -- stealthy, modular, and written in Lua.

The seven organizations include targets in Russia, an airline in China, an embassy in Belgium, and an organization in Sweden. DiMaggio says this is an extremely small number of targets, even for a sophisticated actor. 

"That's exactly why this is so interesting to us," says Jon DiMaggio, senior threat intelligence analyst at Symantec. " ... The fact that someone invested the time and money into creating custom malware and only used it on this many targets." He says targeting this focused means that someone has gone through a lot of trouble and done a lot of reconaissance.  

Symantec has not speculated on Strider's origins or Remsec's creators, other than to say in today's blog announcing the discovery that it is "possible that the group is a nation-state level attacker."

Researchers do acknowledge, however, that the group's attacks have "tentative links" with earlier cyberespionage malware -- Flame, highly sophisticated malware that mostly hit targets in the Middle East and was widely thought to derive from Western sources. Remsec and Flame both use modules written in the Lua programming language, which is a rare technique. 

DiMaggio says that using Lua is one of the Remsec authors' "self-protection mechanisms." Common security tools' usual logic and detection engines are less likely to find uncommon methods like this. It's the same reason, DiMaggio says, that some components of the Remsec malware are in the form of executable blobs (binary large objects), which are also less common. 

"That's what I would do if I was writing malware," says DiMaggio.

It's not the end of Remsec's stealth mechanisms either. According to the Symantec blog, "much of the functionality is deployed over the network, meaning it resides only in a computer's memory and is never stored on disk."

The Lua modules in Remsec include a network loader, host loader, network listener, basic pipe back door, a more advanced pipe back door that can read, write and delete files), an HTTP back door that includes URLs for a command-and-control server, and a keylogger.

The keylogger contains the word "Sauron" in the code -- perhaps named after the Lord of the Rings character and his famous flaming all-seeing eye. Symantec continued with the LOTR theme when they named the threat actor Strider, one of Aragorn's alternate names. 

For the complete indicators of compromise, see here.

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