North Korea is likely behind attacks exploiting a Korean word processing program

The proprietary program, called Hangul Word Processor, is used primarily in the south by the government and public institutions.

The vulnerability, CVE-2015-6585, was patched three days ago by its developer Hancom.

FireEye's conclusion is interesting because only a handful of attacks have been publicly attributed to the secretive nation, which is known to have well-developed cyber capabilities.

One of the most prominent instances was the devastating attack in November 2014 against Sony Pictures, which lost sensitive corporate data and email and saw many of its computers rendered inoperable.

In a rare move, the FBI blamed North Korea for the Sony hack based on an analysis of malware suspected to have been developed by the country and used in other attacks.

FireEye said its attribution wasn't conclusive, but the targeting of a proprietary South Korean software program combined with targets in the country led it to "assess that this activity may be associated with North Korea-based threat actors."

If the malicious HWP file is opened, it installs a backdoor which FireEye nicknamed "Hangman." It's used for downloading files and probing file systems.

Once Hangman has collected data, it sends it to command-and-control servers over an SSL (Secure Sockets Layer) connection. The IP addresses of those servers are hard-coded into Hangman and have been linked to other suspected North Korea-related attacks.

Hangman is also similar to another backdoor FireEye calls Peachpit, which may have been developed by North Korea, the report said.