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Step-by-step by the Cash Message ransomware – Sophos Information


In August 2023, the Sophos X-Ops Incident Response workforce was engaged to help a company in Australia contaminated with Cash Message ransomware.  This assault vector, identified for its stealth, doesn’t append any file extensions to the encrypted knowledge, making it tougher for victims to determine the encrypted recordsdata just by recognizing such extensions.  

On this publish, we are going to have a look at the incident assault stream, illustrating how menace actors are deploying the Cash Message ransomware and what measures can fight attacker efforts at varied factors alongside the MITRE ATT&CK chain. 

Make a remark of it 

As a part of its routine, the ransomware drops a ransom be aware named “money_message.log” instantly into the basis listing of the C: drive.  

The ransom be aware on the goal’s system learn as follows: 

Your recordsdata was encrypted by “Cash message” worthwhile group and might’t be accessed anymore. 

When you pay ransom, you’ll get a decryptor to decrypt them. Don’t attempt to decrypt recordsdata your self – in that case they are going to be broken and unrecoverable. 

For additional negotiations open this <redacted>.onion/<redacted> 

utilizing tor browser https://www.torproject.org/obtain/ 

In case you refuse to pay, we are going to publish the recordsdata we stole out of your inside community, in our weblog: 

<redacted>.onion 

Encrypted recordsdata can’t be decrypted with out our decryption software program. 

<redacted>.onion/<redacted> 

Assault Circulation Particulars 

Preliminary Entry 

Our investigation signifies that the attacker gained preliminary entry through the goal’s VPN, which was  utilizing single-factor authentication. That is an instance of MITRE’s T1078 – Legitimate Accounts approach. 

Steerage 

Implementing multifactor authentication (MFA) for VPN connections is paramount to boost safety and thwart potential unauthorized entry. Moreover, steady monitoring of VPN logs and person exercise must be in place to promptly detect any suspicious login makes an attempt or anomalies. Upgrading to a extra sturdy and layered authentication method, similar to MFA, is crucial to bolster the primary line of protection towards potential menace actors searching for to use single-factor vulnerabilities and acquire unauthorized VPN entry. 

Protection Evasion 

The menace actor deployed GPO Coverage to disable Home windows Defender real-time safety. That is an instance of MITRE’s T1562.001: Impair Defenses: Disable or Modify Instruments sub-technique. 

[HKEY_LOCAL_MACHINESoftwarePoliciesMicrosoftWindows Defender] DisableAntiSpyware: [REG_DWORD_LE] 1 
[HKEY_LOCAL_MACHINESoftwarePoliciesMicrosoftWindows DefenderReal-time Protection] DisableRealtimeMonitoring: [REG_DWORD_LE] 1 

Steerage 

The primary line of protection accessible to organizations is to make use of a safety agent that has sturdy tamper safety. When it comes to monitoring for this exercise, these are detection-ready occasion sources. Whereas it’s potential a system administrator would disable these protections (at the very least quickly) throughout troubleshooting, given the danger of this exercise, it’s one thing that must be investigated promptly if a corresponding help ticket isn’t discovered. 

Lateral Motion 

The menace actor leveraged psexec to run a batch script with the intention of enabling the RDP port, subsequently utilizing Distant Desktop Protocol (RDP) to traverse the community. That is an instance of MITRE’s T1021.001: Distant Companies: Distant Desktop Protocol sub-technique. RDP is a typical discovering in circumstances dealt with by Incident Response, as proven by our findings from IR circumstances dealt with through the first half of 2023. 

A pie chart showing percentages of RDP abuse seen in cases handled by Sophos X-Ops' IR team during the first half of 2023. Internal findings = 78%; internal and external = 17%; external-only = 1%. No RDP abuse was observed in 4% of cases.

Determine 1: RDP abuse detections in IR circumstances for the primary half of 2023 

The batch script contents are as follows:

reg add "HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlTerminal Server" /v fDenyTSConnections /t REG_DWORD /d 0 /f 
Allow-NetFirewallRule -DisplayGroup 'Distant Desktop' 
netsh advfirewall firewall add rule title="Open Distant Desktop" protocol=TCP dir=in localport=3389 motion=enable 

Steerage 

Securing RDP entry may be tough for a lot of firms, however it’s a challenge worthy of funding. The primary merchandise to test off the field is to limit, by function, which accounts can entry different techniques utilizing RDP. The overwhelming majority of customers don’t want this entry. Secondly, adopting a centralized bounce server, which solely admins can entry with MFA and blocking on the community stage different system-to-system RDP is a robust preventative management. Lastly, a detection must be in place to promptly overview anomalous RDP connections to deconflict them with permitted system administration exercise. 

Credential Entry 

The menace actor, utilizing Secretsdump.py (a part of the Impacket toolkit), retrieved the SAM registry hive. That is an instance of a technique of executing MITRE’s T1003.002: OS Credential Dumping: Safety Account Supervisor subtechnique. 

C:WINDOWSsystem32svchost.exe -k localService -p -s RemoteRegistry 

Steerage 

It’s essential for organizations to prioritize the safeguarding of delicate credentials. Implementing robust entry controls, using sturdy endpoint detection and response options, and monitoring for any suspicious exercise associated to SAM hive entry are important steps. Any unauthorized makes an attempt to entry or manipulate this crucial system part must be promptly investigated, as they could point out a breach or malicious exercise that might compromise the safety of delicate credentials. 

 Assortment 

A confirmed compromised account was used to entry delicate folders like Finance, Payroll, SalesReport and HR in FileServer. MITRE lists 37 sub- and sub-sub-techniques beneath TA0009: Assortment. 

Steerage 

Usually by the point a menace actor is staging knowledge, it’s too late to have a superb safety consequence. method to stop theft of information is to undertake least-privilege entry, which suggests guaranteeing solely the required individuals have entry, adopted by granular controls on exporting, sharing, or transferring the recordsdata. DLP options, whereas having a historical past of being tough to implement and keep, are price evaluating for high-risk knowledge. 

 Exfiltration 

The menace actor leveraged MEGAsync to exfiltrate the info. That is an instance of MITRE’s T1567.002: Exfiltration Over Internet Service: Exfiltration to Cloud Storage. 

UserAssist entry: 87 Worth title: C:Customers<redacted>AppDataLocalTemp6MEGAsyncSetup32.exe  

Depend: 1  

Person ”<redacted> registered Activity Scheduler job “MEGAMEGAsync Replace Activity S-1-5-21-<redacted>" 

Steerage 

Organizations ought to give attention to enhancing knowledge loss prevention measures and community monitoring. Implementing sturdy outbound site visitors evaluation and content material inspection may also help determine and block suspicious knowledge transfers. Moreover, intently monitoring MEGAsync actions and detecting any uncommon or unauthorized knowledge transfers may be important in mitigating knowledge breaches. Quickly examine and reply to any indicators of unauthorized exfiltration to stop potential knowledge compromise and decrease the impression on knowledge confidentiality. 

Influence 

The menace actor leveraged two ransomware binaries, one for the Home windows surroundings and one for the Linux surroundings. The Home windows model is called home windows.exe, and is detected as Troj/Ransom-GWD by Sophos. That is an instance of MITRE’s T1486: Information Encrypted for Influence. 

  • The Cash Message encryptor is written in C++ and contains an embedded JSON configuration file which incorporates some key particulars like what folders to dam from encrypting, what extension to append, what providers and processes to terminate, and area login names and passwords probably used to encrypt different units. 
  • The encryptor makes use of the ChaCha Quarter Spherical algorithm and ECDH encryption 
  • The ransomware creates the C:money_message.log ransom be aware when full 
  • On endpoints protected with Sophos, the next detection is triggered: 

Malware detected: ‘Troj/Ransom-GWD’ at ‘C:Customers<redacted>AppDataLocalTemp6windows.exe’ 

The Linux variant is called ‘esxi’, Upon execution it’s going to delete all of the digital arduous disks. That is an instance of MITRE’s T1561: Disk Wipe. 

 Instructions executed on ESXi host: 

cd /tmp/ 
chmod 777 esxi 
dir 
ls 
./esxi 

Steerage 

As talked about earlier, at this late stage within the assault, having full protection on all techniques with a correctly configured XDR answer is significant to guard organizations from ransomware. Within the case of Sophos, it’s crucial for patrons to have their CryptoGuard coverage activated, which is one thing help can information clients on. 

Conclusion 

The Cash Message attackers’ path to exfiltration conforms to a reasonably typical MITRE ATT&CK chain, as we’ve proven above. Although this explicit attacker tries to muddy the waters for defenders, good protection – particularly within the early phases – can present an efficient toolkit towards unhealthy outcomes. 

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