The Ryuk Threat: Why BazarBackdoor Matters Most

By The Cofense Intelligence TeamYesterday, the Cofense Intelligence team released the following guidance via a flash alert to Cofense Intelligence customers.

On October 28, media reports and U.S. government notifications emerged regarding an active “credible” Ryuk ransomware threat targeting the U.S. healthcare and public health sector, with plans of a coordinated attack October 29. This was reportedly based on chatter observed in an online forum that allegedly included members of the group behind Ryuk. Cofense Intelligence is conducting an ongoing investigation into this threat. While we can’t evaluate the government’s determination of this threat as credible, we are taking this very seriously and have observed increased activity against the healthcare sector. We assess with high confidence that BazarBackdoor is the primary delivery mechanism currently used for Ryuk operations. Moreover, we’ve identified that similar phishing campaigns used to establish a foothold for Ryuk infections have targeted other sectors, as well.

BazarBackdoor: Ryuk’s Inroad

Cofense Intelligence assesses that Ryuk operators typically wait until their preferred delivery mechanism is successfully deployed to an intended target prior to deploying Ryuk ransomware itself. Up until TrickBot’s disruption, Ryuk was most frequently delivered via TrickBot. However, our analysis indicates that the group behind Ryuk began leveraging BazarBackdoor to establish access to target systems in September. This aligns closely with announcements that U.S. Cyber Command had taken action to disrupt TrickBot operations. In recent weeks, we assess with high confidence that BazarBackdoor has been Ryuk’s most predominant loader. With lower confidence, we assess this wave of Ryuk activity may be, in part, in retaliation for September’s TrickBot disruptions.

BazarBackdoor is a stealthy malware downloader that we assess is used by the same group as TrickBot. Typically, emails designed to appear as internal business communications are sent to victims within an organization, often with relevant employee names or positions. These emails usually contain a link, most often to a Google Docs page, though other well-known file hosting platforms have also been used. The Google Docs page will then present a convincing image with another embedded link. This link is typically to a malicious executable hosted on a trusted platform such as Amazon AWS. This chain of legitimate services makes it difficult to detect and stop these campaigns.

Once in place on a victim’s computer, BazarBackdoor uses specialized network communications to avoid detection and to contact its command and control (C2) locations. Part of these communications involve DNS lookups for .bazar domains, which is the reason behind its Bazar name. These C2 locations also often serve as payload locations. After BazarBackdoor contacts its C2 center it will then collect additional information which the threat actors can use to deliver customized reconnaissance tools, such as Cobalt Strike payloads. The threat actors can also choose to deliver other payloads such as Ryuk ransomware. The deployment of Ryuk ransomware isn’t automated, and therefore won’t occur unless the threat actors decide the infected environment is a target.

All of us should pay special heed to any indications of BazarBackdoor compromise. Regardless of whether recent activity is in retaliation against TrickBot’s disruption, what is clear is that recent efforts by multiple parties to cripple TrickBot seem to have been effective in transitioning the Ryuk actors to leveraging BazarBackdoor. We must be mindful that there are past connections between TrickBot activity and Emotet. While there is no direct evidence of current Emotet involvement in these campaigns, we cannot rule out future delivery of Ryuk via Emotet, given historical relationships between TrickBot and Emotet. As the TrickBot infrastructure appears to be in the process of restructuring, we assess that it may find use again as a delivery mechanism. As a network defender, all three malware families should be prioritized when searching for possible compromises, with the highest priority placed on detections of BazarBackdoor in the near future.

Figure 1: Common Phishing Example Delivering BazarBackdoor

The Phish

Cofense Intelligence has directly identified several campaigns, targeting multiple sectors across our customer base, that share strong similarities to the phishing emails reportedly used as initial attack vectors in Ryuk campaigns, as outlined by FireEye. Two subject themes stand out across several industry verticals we’ve confirmed were targets of BazarBackdoor. These subjects relate A) to employment termination, almost always including the word “termination,” or B) to payroll, almost always including the word “debit,” as shown in Figure 1. While the subjects remain the same, we observed two separate download services: via Google Docs or Constant Contact. The following list highlights the different industries we have confirmed were targeted by such campaigns. However, we cannot assess whether Ryuk operators intended to further infect these targets with Ryuk ransomware. It appears very likely that Ryuk operators have cast a wide net for potential infection vectors, and choose which successful footholds to manually interact with and leverage.

Figure 2: Termination List Phishing Example Delivering BazarBackdoor

It is worth noting that these campaigns began in mid-September, which corresponds with the timing of coordinated offensive operations to disrupt TrickBot. The sectors we have directly observed targeted in these campaigns include:

• Consumer Goods
• Healthcare
• Mining
• Energy
• Insurance
• Professional Services
• Financial Services
• Manufacturing
• Retail

Assessing the Threat

As of early this morning, on October 30, there are reports of some ransomware attacks against U.S. healthcare organizations yesterday. It is possible more reports will emerge in the coming days, though initial indications suggest a healthcare sector doomsday was avoided. In recent weeks, there was an abundance of ransomware activity against the healthcare sector, and we identified an increase in BazarBackdoor targeting. It’s not for us to say whether the stated time or scope of the threat was off base, if there have been active successful countermeasures, or that the flurry of reporting has deterred some ransomware activity for now. It is possible they did/do not want to face such a well-guarded and prepared target base. Still, we are confident that Ryuk operations have recently increased, and that other sectors have come into the crosshairs of potential future Ryuk operations. It’s our assessment that the threat should be taken seriously.

Cofense Intelligence customers have received relevant indicators of compromise (IOCs) and Active Threat Reports (ATRs) as these campaigns are identified and analyzed, and some of these ATRs were first sent in September. Customers can find these ATRs and IOCs in ThreatHQ and via our API, and can access the most up to date list of all relevant Cofense Intelligence IOCs and ATRs tied to BazarBackdoor, TrickBot and Emotet via our API and on ThreatHQ.

For all readers, below is a table of relevant IOCs and Yara Rules associated with BazarBackdoor that can help your organization identify related emails should you be targeted. Gain free access to our intel here.

Register now for our live 30 minute briefing on Ryuk Ransomware & What you need to know on Thursday, November 12 at 11:00 am EST.  Listen is as our Cofense Intelligence team provides the latest insights on this threat and learn how you can protect your organization.

Yara Rules for Campaign Detection 

Rule 1: 

rule PM_Intel_Ryuk_Payload_1029201 {
meta:
  description = “EDR rule for detecting Ryuk ransomware main payload”
strings:
  $ = “.RYK” wide nocase
$ = “RyukReadMe.html” wide nocase
$ = “UNIQUE_ID_DO_NOT_REMOVE” wide nocase
$ = “\users\Public\finish” wide nocase
$ = “\users\Public\sys” wide nocase
$ = “\Documents and Settings\Default User\finish” wide nocase
$ = “\Documents and Settings\Default User\sys” wide nocase
condition:
  uint16(0) == 0x5a4d and uint32(uint32(0x3c)) == 0x00004550 and all of
them
}  

Rule 2:¹ 

rule crime_win64_backdoor_bazarbackdoor1 {
meta:
description = “Detects BazarBackdoor injected 64-bit malware”
author = “@VK_Intel“
reference = “https://twitter.com/pancak3lullz/status/1252303608747565057“
tlp = “white”
date = “2020-04-24”
strings:
$str1 = “%id%”
$str2 = “%d”
$start = { 48 ?? ?? ?? ?? 57 48 83 ec 30 b9 01 00 00 00 e8 ?? ?? ?? ?? 84 c0 0f ?? ?? ?? ?? ?? 40 32 ff 40 ?? ?? ?? ?? e8 ?? ?? ?? ?? 8a d8 8b ?? ?? ?? ?? ?? 83 f9 01 0f ?? ?? ?? ?? ?? 85 c9 75 ?? c7 ?? ?? ?? ?? ?? ?? ?? ?? ?? 48 ?? ?? ?? ?? ?? ?? 48 ?? ?? ?? ?? ?? ?? e8 ?? ?? ?? ?? 85 c0 74 ?? b8 ff 00 00 00 e9 ?? ?? ?? ?? 48 ?? ?? ?? ?? ?? ?? 48 ?? ?? ?? ?? ?? ?? e8 ?? ?? ?? ?? c7 ?? ?? ?? ?? ?? ?? ?? ?? ?? eb ?? 40 b7 01 40 ?? ?? ?? ?? 8a cb e8 ?? ?? ?? ?? e8 ?? ?? ?? ?? 48 8b d8 48 ?? ?? ?? 74 ??}
$server = {40 53 48 83 ec 20 48 8b d9 e8 ?? ?? ?? ?? 85 c0 75 ?? 0f ?? ?? ?? ?? ?? ?? 66 83 f8 50 74 ?? b9 bb 01 00 00 66 3b c1 74 ?? a8 01 74 ?? 48 8b cb e8 ?? ?? ?? ?? 84 c0 75 ?? 48 8b cb e8 ?? ?? ?? ?? b8 f6 ff ff ff eb ?? 33 c0 48 83 c4 20 5b c3}
condition:
( uint16(0) == 0x5a4d and ( 3 of them ) ) or ( all of them )
} 

¹Sourced from https://twitter.com/VK_Intel/status/1315663046694625286 and evaluated by Cofense Intelligence analysts. 

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