Threat Signal Report

Newly Identified Green Stone Malware Leveraging Malicious Macros in Global Campaign

description-logo Description

FortiGuard Labs is aware of a campaign targeting Iranian interests, specifically in the energy sector. Dubbed Green Stone, this malware is delivered through Microsoft Excel spreadsheets containing malicious macros. The Green Stone malware is obfuscated in Base64, where the macro code contains instructions to unpack Green Stone into a temporary directory where it is then executed.


What is Green Stone?

Green Stone is classified as an infostealer, is persistent and will steal information from the affected machine. It will look for specific registry entries in \Microsoft\Internet Explorer\TypedURLs to look for websites that the targeted machine recently visited. Besides containing basic infostealer functionality, Green Stone also connects to Telegram to send C2 traffic through, which is likely a way to evade detection.


The threat has the ability to collect information about the victim machine, take screenshots and send it to a predetermined URI. Green Stone can do the following:


Scan directory hierarchies

Delete files and folders

Run commands

Locate files

Rename files and directories

Copy files

and Unzip


Based on our data, connections to the C2 server reveal the United States accounts for 30 percent, Brazil 15 percent and Argentina, Korea and Germany accounting for less than 2 percent of connections to the 185.162.235[.]184 IP address of the attacker.


Who is Behind Green Stone?

There is not enough information at this time to determine attribution.


Any Other Suggested Mitigation?

As it has been observed that Green Stone threat actors have used malicious Microsoft Office files, likely through social engineering and phishing techniques, it is recommended to never enable macro based documents, especially from a sender that is not recognized.

Due to the ease of disruption and damage to daily operations, reputation, and unwanted release of personally identifiable information (PII), etc. it is important to keep all AV and IPS signatures up to date.


It is also important to ensure that all known vendor vulnerabilities are addressed, and updated to protect from attackers having a foothold within a network. Attackers are well aware of the difficulty of patching and if it is determined that patching is not feasible at this time, an assessment should be conducted to determine risk.


Also - organizations are encouraged to conduct ongoing training sessions to educate and inform personnel about the latest phishing/spear phishing attacks. They also need to encourage employees to never open attachments from someone they don't know, and to always treat emails from unrecognized/untrusted senders with caution. Since it has been reported that various phishing and spear phishing attacks have been delivered via social engineering distribution mechanisms, it is crucial that end users within an organization be made aware of the various types of attacks being delivered. This can be accomplished through regular training sessions and impromptu tests using predetermined templates by an organizations' internal security department. Simple user awareness training on how to spot emails with malicious attachments or links could also help prevent initial access into the network.


What is the Status of Coverage?

Fortinet customers running the latest definitions are protected by the following (AV) signatures:


WM/Agent!tr (Malicious Macro)

W32/Agent.665F!tr (Green Stone)


All network IOC's are blocked by the WebFiltering Client.


Definitions

Traffic Light Protocol

Color When Should it Be used? How may it be shared?

TLP: RED

Not for disclosure, restricted to participants only.
Sources may use TLP:RED when information cannot be effectively acted upon by additional parties, and could lead to impacts on a party's privacy, reputation, or operations if misused. Recipients may not share TLP:RED information with any parties outside of the specific exchange, meeting, or conversation in which it was originally disclosed. In the context of a meeting, for example, TLP:RED information is limited to those present at the meeting. In most circumstances, TLP:RED should be exchanged verbally or in person.

TLP: AMBER

Limited disclosure, restricted to participants’ organizations.
Sources may use TLP:AMBER when information requires support to be effectively acted upon, yet carries risks to privacy, reputation, or operations if shared outside of the organizations involved. Recipients may only share TLP:AMBER information with members of their own organization, and with clients or customers who need to know the information to protect themselves or prevent further harm. Sources are at liberty to specify additional intended limits of the sharing: these must be adhered to.

TLP: GREEN

Limited disclosure, restricted to the community.
Sources may use TLP:GREEN when information is useful for the awareness of all participating organizations as well as with peers within the broader community or sector. Recipients may share TLP:GREEN information with peers and partner organizations within their sector or community, but not via publicly accessible channels. Information in this category can be circulated widely within a particular community. TLP:GREEN information may not be released outside of the community.

TLP: WHITE

Disclosure is not limited.
Sources may use TLP:WHITE when information carries minimal or no foreseeable risk of misuse, in accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction.