On October 28, 2020, the Cybersecurity and Infrastructure Security Agency (CISA), the Federal Bureau of Investigation (FBI), and the Department of Health and Human Services (HHS) issued a joint cybersecurity advisory entitled “Ransomware Activity Targeting the Healthcare and Public Health Sector” (updated on October 29, 2020) that “describes the tactics, techniques, and procedures (TTPs) used by cybercriminals against targets in the Healthcare and Public Health Sector (HPH) to infect systems with ransomware, notably Ryuk and Conti, for financial gain.”
The joint cybersecurity advisory warned: “CISA, FBI, and HHS have credible information of an increased and imminent cybercrime threat to U.S. hospitals and healthcare providers. CISA, FBI, and HHS are sharing this information to provide warning to healthcare providers to ensure that they take timely and reasonable precautions to protect their networks from these threats.
• CISA, FBI, and HHS assess malicious cyber actors are targeting the HPH Sector with TrickBot and BazarLoader malware, often leading to ransomware attacks, data theft, and the disruption of healthcare services.
• These issues will be particularly challenging for organizations within the COVID-19 pandemic; therefore, administrators will need to balance this risk when determining their cybersecurity investments.”
The cybercriminal enterprise behind TrickBot, which is likely also the creator of BazarLoader malware, has continued to develop new functionality and tools, increasing the ease, speed, and profitability of victimization. These threat actors increasingly use loaders—like TrickBot and BazarLoader (or BazarBackdoor)—as part of their malicious cyber campaigns. Cybercriminals disseminate TrickBot and BazarLoader via phishing campaigns that contain either links to malicious websites that host the malware or attachments with the malware. Loaders start the infection chain by distributing the payload; they deploy and execute the backdoor from the C2 server and install it on the victim’s machine.
In early 2019, FBI began to observe new TrickBot modules named Anchor, which cyber actors typically used in attacks targeting high-profile victims—such as large corporations. These attacks often involved data exfiltration from networks and point-of-sale devices. As part of the new Anchor toolset, TrickBot developers created anchor_dns, a tool for sending and receiving data from victim machines using Domain Name System (DNS) tunneling.
anchor_dns is a backdoor that allows victim machines to communicate with command and control (C2) servers over DNS to evade typical network defense products and make their malicious communications blend in with legitimate DNS traffic. anchor_dns uses a single-byte XOR cipher to encrypt its communications, which have been observed using key 0xB9. Once decrypted, the string anchor_dns can be found in the DNS request traffic.
Beginning in approximately early 2020, actors believed to be associated with Trickbot began using BazarLoader and BazarBackdoor to infect victim networks. The loader and backdoor work closely together to achieve infection and communicate with the same C2 infrastructure. Campaigns using Bazar represent a new technique for cybercriminals to infect and monetize networks and have increasingly led to the deployment of ransomware, including Ryuk. BazarLoader has become one of the most commonly used vectors for ransomware deployment.
Once dropped, Ryuk uses AES-256 to encrypt files and an RSA public key to encrypt the AES key. The Ryuk dropper drops a .bat file that attempts to delete all backup files and Volume Shadow Copies (automatic backup snapshots made by Windows), preventing the victim from recovering encrypted files without the decryption program. In addition, the attackers will attempt to shut down or uninstall security applications on the victim systems that might prevent the ransomware from executing. Normally this is done via a script, but if that fails, the attackers are capable of manually removing the applications that could stop the attack. The RyukReadMe file placed on the system after encryption provides either one or two email addresses, using the end-to-end encrypted email provider Protonmail, through which the victim can contact the attacker(s). While earlier versions provide a ransom amount in the initial notifications, Ryuk users are now designating a ransom amount only after the victim makes contact. The victim is told how much to pay to a specified Bitcoin wallet for the decryptor and is provided a sample decryption of two files.
Initial testing indicates that the RyukReadMe file does not need to be present for the decryption script to run successfully but other reporting advises some files will not decrypt properly without it. Even if run correctly, there is no guarantee the decryptor will be effective. This is further complicated because the RyukReadMe file is deleted when the script is finished. This may affect the decryption script unless it is saved and stored in a different location before running.
CISA, FBI and HHS do not recommend paying ransoms. Payment does not guarantee files will be recovered. It may also embolden adversaries to target additional organizations, encourage other criminal actors to engage in the distribution of ransomware, and/or fund illicit activities.
In addition to TrickBot and BazarLoader, threat actors are using malware, such as KEGTAP, BEERBOT, SINGLEMALT, and others as they continue to change tactics, techniques, and procedures in their highly dynamic campaign.
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