Saturday, April 13, 2024

DarkGate Malware Abusing Cloud Storage & SEO Following Delivery Over Teams

DarkGate loader delivery surged after the Qakbot takedown, with financially motivated actors like TA577 and ransomware groups (BianLian, Black Basta) using it to target financial institutions (US, Europe) for double extortion. 

It establishes an initial foothold and deploys info-stealers, ransomware, and remote access tools to maximize data exfiltration and extortion gains by utilizing legitimate channels (DoubleClick ads, cloud storage) and phishing emails for distribution. 

Overview of DarkGate version 5 activity
Overview of DarkGate version 5 activity

Similarities with IcedID delivery methods suggest that threat actors may be cooperating or sharing their tradecraft.

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DarkGate is a malware-as-a-service advertised in June 2023 that offers remote access, data theft, and privilege escalation by using multiple techniques to evade, including a custom crypter, polymorphism, and anti-VM. 

Persona RastaFarEye is advertising DarkGate on a cybercrime forum.
Persona RastaFarEye is advertising DarkGate on a cybercrime forum.

It also utilizes LOLBAS tools to download a malicious AutoIt script that decrypts the DarkGate payload, injects it into a process, and establishes persistence through registry keys and a rootkit module.  

DarkGate infection chain through PDF lure. 
DarkGate infection chain through PDF lure. 

Attackers primarily target financial institutions like BDK, a major German bank, using phishing emails with lures relevant to the target’s industry and delivering the DarkGate payload through embedded links in PDF attachments. 

The delivered malicious PDF attachment targeted the BDK. 
The delivered malicious PDF attachment targeted the BDK. 

The links redirect victims to download pages hosted on compromised websites.

To evade detection, DarkGate operators have incorporated innovative techniques like abusing DNS TXT records to execute malicious Windows commands that download and install the malware.  

 Malware delivery similarities between DarkGate and IcedID.
 Malware delivery similarities between DarkGate and IcedID.

EclecticIQ analysts compared DarkGate and IcedID malware, finding shared tactics like obfuscated strings, using PING.exe to check internet connectivity, CURL.exe for downloading payloads, and decoy PDF documents. 

They differed in execution tools (DarkGate: Cscript.exe, IcedID: Rundll32.exe) and payload types (DarkGate: VBS script, IcedID: disguised DLL). 

Showing the example of DoubleClick Ad service abuse.
Showing the example of DoubleClick Ad service abuse.

For DarkGate delivery, attackers abused open redirects in Google’s DoubleClick ads with emails containing links disguised as invoices.

Since January 2024, DarkGate has shifted to CAB and MSI formats, likely to evade detection. 

DarkGate version 6.1.6 employs DLL side-loading for evasion, where a malicious DLL is loaded into legitimate applications (e.g., VLC, iTunesHelper) through a compromised MSI installer. 

Dropped DarkGate payloads
Dropped DarkGate payloads

The payload then decrypts itself using a key within a fake sqlite3.dll and drops a script into C:\temp, while decrypting again using a separate key and launching the final DarkGate payload. 

Decrypted configuration reveals the command-and-control server.
Decrypted configuration reveals the command-and-control server.

The version also features a new configuration decryption routine using XOR encryption to hide C2 server information and other operational parameters, making it more difficult for signature-based detection. 

DarkGate is a Malware-as-a-Service (MaaS) that steals information like usernames, CPU information, and anti-virus information from the victim device after gaining an initial foothold. 

Decrypted C2 activity showing the version of Darkgate.
Decrypted C2 activity showing the version of Darkgate.

It then uses Living Off the Land Binaries (LOLBAS) like wscript.exe and cscript.exe to execute a VBS script. 

BianLian ransomware attack chain using DarkGate.

Network traffic analysis can be used to detect suspicious patterns like downloads from unusual domains or suspicious Curl.exe activity and YARA rules can also be used to detect the final payload on the infected device.  

The IOCs include suspicious user agent strings, command and control (C2) server domains, payload downloader URLs with malicious zip files, and multiple file hashes, which can be used to identify infected systems, block malicious traffic, and improve threat detection. 

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Guru baran
Guru baran
Gurubaran is a co-founder of Cyber Security News and GBHackers On Security. He has 10+ years of experience as a Security Consultant, Editor, and Analyst in cybersecurity, technology, and communications.

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