Crypt ‘n’ Leak

New ransomware trend exploits vulnerability in Hong Kong’s VPNs

The fast pace of criminals’ innovation is an ever-recurring theme in cyber security. When the cybercriminal underground economy is particularly saturated, threat actors will likely be driven to explore new ways to differentiate their offering in the illicit cybercriminal market and increase revenue. This is what we are currently observing among ransomware operators. Many ransomware variants have been released in recent years. In the last several months, however, a smaller group of ransomware-as-a-service providers emerged with new a tactic to extort their victims.

DarkLab’s Threat Intelligence team is currently tracking multiple ransomware groups that, in addition to encrypting victims’ data, also steal sensitive files and threaten their public release if ransom demands are not met. The extortionists’ goal is to apply additional pressure on victims by threatening reputational damage and potential regulatory fines if sensitive data is leaked, on top of hindering systems availability.

DarkLab incident response team has observed multiple such incidents affecting Hong Kong organisations, highlighting how ransomware leak attacks are a significant and current threat for companies in the region as well as globally. DarkLab has experience in dealing with Maze and NetWalker ransomware attacks in Hong Kong. This article aims to first shed light on each malware’s background, and then to discuss some of the tactics, techniques, and procedures (TTPs) we observed in our incident response investigations.

The RaaS model and its implications

Maze and NetWalker ransomware variants are developed by a core group of cybercriminals and then leased to other criminal operators, called affiliates, on deep and dark web forums. This model is usually referred to as ransomware-as-a-service (RaaS), where operators and developers share profits in an agreed percentage.

RaaS means that different operators of the same ransomware group can target multiple companies at the same time, regardless of their size or geographical location. Ransomware operators are independent actors, so they may differ in the attack tactics exploited. This makes the job of network defenders more challenging because of the larger set of potential tactics, techniques, and procedures (TTPs) to mitigate.

Some RaaS developers, like those of NetWalker, only accept affiliates with proven technical skills and existing access to multiple corporate networks. Stricter cybercriminal candidate screening is leading to an increase in targeted ransomware attacks exploiting external network systems. Exposed remote desktop protocol (RDP) and vulnerable internet-facing services are increasingly more likely entry points than untargeted phishing emails.

The rise of crypt and leak

Since the end 2019, some ransomware groups have begun threatening to release sensitive victim’s data if their ransomware demand are not met. Maze went a step further and set up a dedicated website to publicly shame victims and leak data. More groups, including NetWalker, are now maintaining their own leak websites on the clearnet or on tor hidden services. DarkLab is currently tracking 13 ransomware leak websites, highlighting the rapidly increasing scale of this crypt and leak trend.

This new pressure tactic by ransomware operators has significant implications for companies. Previously, an efficient back-up policy would potentially guarantee a timely recovery from ransomware attacks. Now that ransomware groups also leak data, back-ups are not enough anymore. Organisations must ensure that sound cyber security hygiene is maintained at all times to prevent a ransomware intrusion from taking place at all.

Maze

Maze ransomware appeared in May 2019, but it began leaking victim’s data only in 2020. The group maintains two sites, one to publish victim data (see figure 1), the other to communicate with its victims and let them decrypt some test files (see figure 2). Both have a back-up tor hidden service counterpart to avoid take down by law enforcement.

Figure 1 – redacted screenshot of Maze ransomware leak site

Figure 2 – Screenshot of Maze ransomware chat site

Figure 3 – Geography of Maze’s victims posted on their site

Figure 4 – Sectorial breakdown of Maze’s victims posted on their site

NetWalker

NetWalker ransomware is based on a previous variant called Mailto and was rebranded in its current name in March 2020, despite little change in its code. The developers of NetWalker recruit affiliates on Russian-language cybercriminal forums and particularly look for individuals with network intrusion experience. The group has allegedly been very successful since its inception. NetWalker developers claimed to have gained millions of US dollars since March, although it remains unclear whether this is just an exaggeration to attract more affiliates to their program or not.

NetWalker also operates a website that lists their victims and leaks their data. We noticed that the group behind NetWalker selectively deletes victims’ entries from their website overtime, so the range of targeted organisations is likely more extensive than that presented in the graphs below.

Figure 5 – Redacted screenshot of NetWalker ransomware leak site

Figure 6 – Geographical breakdown of NetWalker’s victims posted on their site, more have likely been targeted and not posted online or deleted from existing victims’ list

Figure 7 – Sectorial breakdown of NetWalker’s victims posted on their site, more sectors have likely been targeted

Observed tactics, techniques, and procedures

DarkLab incident response investigations found that operators of both Maze and Ransomware exploited a known Pulse Secure VPN vulnerability – CVE-2019-11510 – to gain initial access to victims in Hong Kong. The same vulnerability has been exploited by multiple ransomware groups against other high profile targets, including by Sodinokibi against Travelex in January.

In both cases, the remote access technology SSLVPN was Active Directory (AD) authenticated, giving attackers a legitimate network account early on in their intrusion. Once inside the victim’s network, the attackers would conduct enumeration and other reconnaissance activities by, for instance, searching for password files in share folders. The attackers will also actively look for idle and vulnerable servers with intentions to expand their foothold.

During our investigations we found that both intruders used common hacking tools, although with some differences. Tools observed include windows administration tools like psexec, open source tools for lateral movement like crackmapexec, PowerShell versions of Mimikatz and PowerView for credential theft, further enumeration and privilege escalation, as well as off-the-shelf network scanners. 

The Maze and NetWalker operators eventually managed to obtain access to administrator accounts, which allowed them in both cases to disable anti-virus solutions on network end points. Similarly, creation of new domain administrator accounts allowed them persistence on the network. 

From such privileged positions the operators staged malware and other required artefacts on accessible locations in the victims’ networks, such as shared folders – for NetWalker – and NETLOGON folders – for Maze. We suspect that in both incidents scripts were used to automatically spread the ransomware in the network.

In the case of Maze, the deployment script would also disable endpoints’ protection software, and enable services, such as Windows Remote Management, that would allow re-entry. Maze operators also abused group policy objects (GPOs) to weaken their endpoint defences by changing configurations, and to redeploy the malware to new machines. The latter would ensure that the ransomware would also spread to endpoints after they shut down or if they joined the network at a later time.

Conclusion

The double extortion of crypt and leak groups and the growing trend of targeted attacks against external network infrastructure makes ransomware leaks one of the most significant threats to companies, regardless of sectors. The recent targeting of Hong Kong organisations by Maze and NetWalker also reaffirms how the SAR’s threat landscape is closely associated with threat trends worldwide.

Companies in Hong Kong should therefore adopt a proactive approach to review their security posture and avoid targeted network intrusions in the first place. Presence of timely back-ups can help restore system availability but it is not an effective mitigation against the increasing threat of ransomware data leak. Organisations should also focus on maintaining situational awareness on developments in the global threat landscape, as threats to companies abroad are likely to quickly become threats to Hong Kong organisations too.

Indicators of Compromise

HashFile nameDescription
c45ebccb7dc2bbc34c51c82c3eba6448apply.ps1Generates GPO package to disable AV, settings
16b5ddd25bb610270e52c1663931ef4csystem.dllMaze ransowmare
0e7d5d16e03393605f5f4862f1b9cc37crackmapexec.exeLateral movement tool
d6a246a98a0387e2a5f9d95ddd8ae164syspool.exeLightweight network scanner
696bb8648eceaa187cbc1f06205a23cecity.exeNetWalker ransomware
84ddf23d4307b1a9989352f4845d0edecity.ps1NetWalker PowerShell script

Phobos ransomware

Incidents affecting Hong Kong organisations

In the last two months DarkLab Incident Response and Threat Intelligence teams observed multiple incidents in Hong Kong involving the Phobos ransomware variant.

There is no explicit indications that these incidents are part of a campaign targeting Hong Kong. Rather, they are likely due to Phobos’ prevalence in the cybercriminal underground. Nonetheless, the similarities in observed tactics, techniques and procedures (TTPs), and in the ransomware deployed prompted us to release this alert to help companies improve their timely detection and response to this threat.

Intrusions analysis

Phobos shares many similarities with the Dharma ransomware, and has been sold as  ransomware-as-a-service on the cybercriminal underground since at least December 2018. This means that even low skilled threat actors can rent the malware from its developers and spread it via whatever means they have access to. 

According to our DarkLab’s incident investigations, exploitation of remote desktop protocol (RDP) servers and their credentials are the most common infection vectors. In particular, we observed RDP bruteforcing and exploitation of weak password policies as the most frequent attack vectors. Such TTPs match previously reported instances of Phobos intrusions worldwide.

Once inside the victims’ network, we have seen criminals creating a local account with netplwiz, deploying a malicious network share scanner called 5-NS new.exe, and deleting event logs prior to executing the main payload.

Several hours after the initial intrusion threat actors triggered the ransomware in the form of a malicious executable. Other than encrypting the files, the ransomware also tampered with infected hosts to disable the firewall and other security configurations.

Conclusion

Attackers did not employ particularly sophisticated tradecraft and PwC was able to help clients contain the incidents quickly. Nonetheless, the intrusions impaired systems availability and created operational disruption among victim companies. This can be particularly damaging when most organisations’ staff connect remotely to the corporate network due to the COVID-19 pandemic.

Recommendations

To protect against ransomware incidents via RDP exploitation, DarkLab recommends companies to:

  • Ensure visibility over public-facing RDP servers via external scans
  • Limit exposure of public-facing systems whenever possible
  • Enforce use of multi-factor authentication for remote access, particularly RDP
  • Ensure your organisation has and follows an effective back-up policy
File NameMD5Description
20.09.2019Taskmgr.exeb8351ba02dbce02292a01a6e85112e2bPhobos ransomware
Mouse Lock_v22.exefc9c80e1767e1266056b1b2c89a74ce5Blocks mouse cursor on screen
5-NS new.exe597de376b1f80c06d501415dd973dcecNetwork shares scanner