Description of Campaign
The Nerbian remote access trojan is written in the Go programming language, utilizes multiple anti-analysis and anti-reversing techniques, and uses various open-source Go libraries. The malware is distributed in phishing emails with an attached Microsoft Word document and appears to be sent from the World Health Organization. Nerbian gathers and exfiltrates system information, network data, keystrokes, and screen captures.

Our ATR Team gathers and analyzes information from multiple open and closed sources before disseminating intelligence reports. This campaign was researched by Proofpoint and shared publicly.

How to use this article:

1. If a Threat Hunting table has been created, use the rules contained to search for malware related to this campaign. 
2. Review the product detection table and confirm that your environment is at least on the specified content version.
   To download the latest content versions, go to the Security Updates page.
3. Scroll down and review the "Product Countermeasures" section of this article. Consider implementing them if they are not already in place.
4. Review KB91836 - Countermeasures for entry vector threats.
5. Review KB87843 - Dynamic Application Containment rules and best practices.
6. Review KB82925 - Identify what rule corresponds to an Adaptive Threat Protection and Threat Intelligence Exchange event.

Threat Hunting

YARA

rule Nerbian_RAT { meta: author = "ptrouerbach" reference = "5e6c5a9fda2d20125f6f24e37e8a217a39ff0a5cfddc07ddfdb18049d9ea4597" malfamily = "NerbianRAT" strings: $args_p = "p-" ascii $args_s = "s-" ascii $args_h = "h-" ascii $args_P = "P-" ascii $hardcoded_aes_key = { 17E87F581F1DF8D6129D65FD50CEB3DD6C4E1C223077CD7D4C595DA6C3DF92B2 } $param_auth = "auth_post" ascii $param_session = "session_key" ascii $param_data = "data_post" ascii $param_addr = "addr_post" ascii $param_port = "port_post" ascii condition: uint16be(0) == 0x4D5A and ($hardcoded_aes_key or (all of ($param*) and all of ($args*))) and filesize < 10MB }

This Knowledge Base article discusses a specific threat that's being tracked. The list of IOCs will change over time; check Trellix Insights for the latest IOCs.
 
Campaign IOC

Type	Value
SHA256	EE1BBD856BF72A79221BAA0F7E97AAFB6051129905D62D74A37AE7754FCCC3DB
SHA256	5E6C5A9FDA2D20125F6F24E37E8A217A39FF0A5CFDDC07DDFDB18049D9EA4597
HOSTNAME	www.fernandestechnical.com
URL	https://www.fernandestechnical.com/pub/health_check.php
IP-DST	185.121.139.249

Minimum Content Versions

Content Type	Version
V2 DAT (VirusScan Enterprise)	10367
V3 DAT (Endpoint Security)	4819

  
Detection Summary                               

IOC	Scanner	Detection
EE1BBD856BF72A79221BAA0F7E97AAFB6051129905D62D74A37AE7754FCCC3DB	AVEngine V2	W97M/Downloader.duz
	AVEngine V3	W97M/Downloader.duz
	JTI (ATP Rules)	-
	RP Static	-
	RP Dynamic	-

 

IOC	Scanner	Detection
5E6C5A9FDA2D20125F6F24E37E8A217A39FF0A5CFDDC07DDFDB18049D9EA4597	AVEngine V2	Backdoor.gen.aj
	AVEngine V3	Backdoor.gen.aj
	JTI (ATP Rules)	JTI/Suspect.1179887
	RP Static	-
	RP Dynamic	-

Minimum set of Manual Rules to improve protection to block this campaign:

IMPORTANT: Always follow best practices when you enable new rules and signatures.

When you implement new rules or signatures, always set them to Report mode first and check the alerts generated. Resolve any issues that arise and then set the rules to Block. This step mitigates against triggering false positives and allows you to refine your configuration.

For more information, see KB87843 - List of and best practices for Endpoint Security Dynamic Application Containment rules.
Endpoint Security - Exploit Prevention:
Host Intrusion Prevention:
Aggressive set of Manual Rules to improve protection to block this campaign:

IMPORTANT: Always follow best practices when you enable new rules and signatures.

When you implement new rules or signatures, always set them to Report mode first and check the alerts generated. Resolve any issues that arise and then set the rules to Block. This step mitigates against triggering false positives and allows you to refine your configuration.

For more information, see KB87843 - List of and best practices for Endpoint Security Dynamic Application Containment rules.

Host Intrusion Prevention: