eSentire Threat Intelligence Malware Analysis: RedAlert

In recent months, we have seen numerous ransomware operators leveraging double extortion, a type of ransomware attack where the threat actor(s) exfiltrate the data before encrypting it – with an explicit threat to release it publicly if the victim fails to pay.

RedAlert, a new ransomware strain that targets VMware ESXi servers, uses double extortion to increase the pressure on victims and make them pay the ransom within a short period of time. This malware analysis delves deeper into the technical details of how the RedAlert malware functions and our security recommendations to protect your organization from being exploited.

Case Study

RedAlert ransomware also known as N13V is a new strain of ransomware designed to target Linux VMWare ESXi servers. The ransomware is also reported to attack Windows servers but the eSentire Threat Response Unit (TRU) was not able to locate the Windows ransomware samples. On July 5, 2022, MalwareHunterTeam submitted a Twitter post on RedAlert ransomware cybercriminal group leaking the exfiltrated data on one of the victims based in France.

Later, the ransomware actors published the data of another victim, Vahanen Group, which is a construction engineering company (Figure 2).

On July 4, Vahanen Group mentioned that they were undergoing a new type of a ransomware attack. They also mentioned that there were a series of simultaneous attacks going in European companies (Figure 3).

It’s worth mentioning that there was a RedAlert ransomware incident on Windows OS spotted in 2017. The ransomware obtained the code from the Hidden Tear open-source ransomware project. The code is written in .NET and uses AES algorithm for file encryption. However, eSentire TRU could not identify if the same actor is behind both ransomware samples. RedAlert’s (2017) ransom note and wallpaper are shown in Figures 4-5.

RedAlert Technical Analysis

RedAlert ransomware sample is a 64-bit ELF executable. By executing the -h (help) option, we can see that RedAlert provides multiple features including stopping all running Virtual machines, cryptography performance tests, encryption time check (Figure 6). This concludes that the ransomware is designed to run manually by threat actor(s) on the targeted machines.

It is worth noting that to be able to execute the parameters specified in the help section, the attacker(s) need to gain root access on the target machine.

What makes RedAlert different from other types of ransomware is that it leverages NTRUEncrypt for encryption. NTRU is an open-source public-key cryptosystem and is faster than RSA, according to the researchers at Katholieke Universiteit Leuven in Belgium. The encryption algorithm is also not susceptible to known quantum attacks due to its lattice-based nature, which means that Shor’s algorithm is not applicable, as NTRU does not rely on factoring large integers. Only FiveHands ransomware is known to use NTRUEncrypt so far.

The RedAlert ransomware runs the asymmetric cryptography performance checks and chooses the fastest encryption parameter from the given set:

For each parameter, RedAlert performs the encryption (enc) and decryption (dec) for the amount of operations performed per second. The performance checks also measure the time for the key generation, appending the keygen string to it (Figure 7).

The ransomware is leveraging ESXCLI command set to kill the virtual machine. First, it lists the virtual machines on the target system with the vm process list command. Then, it forcibly kills the virtual machines using the command vm process kill, where world-id parameter is the World ID (equivalent to process ID) of the virtual machine to kill (Figure 10).

Despite the capability to encrypt any file extension, RedAlert only targets the following file extensions that are only specific to VMWare:

• .log
• .vmdk
• .vmem
• .vswp
• .vmsn

RedAlert adds the .crypt658 extension to the encrypted files. For each file type mentioned above, RedAlert generates a new symmetric 44-byte encryption key which is randomly generated using the function call ntu_rand_generate. The symmetric key is then encrypted with NTRU local public key.

Next, the ChaCha20 symmetric encryption CTX initialization starts, where the contents of the file get encrypted with ChaCha20 (a 256-bit cipher) along with the symmetric key and get written to the end of the encrypted file with a 16-byte authentication tag (Figure 11).

During the encryption process, RedAlert appends the unique identifier to each victim as shown in Figure 12. The unique identifier value (which will always be 1643 bytes) is also written to the configuration file generated and placed in the root directory prior to the file encryption process. The configuration filename is built on the SHA-1 hash value of the hardcoded public key.

The hardcoded public key is used to encrypt the local private key within the init_crypto_params function, where local public/private NTRU key pair is randomly generated (Figure 13). The configuration file stores the public key and encrypted local private key. If the configuration file does not exist, RedAlert generates a new one and it will use it each time during file encryption process.

The hex string representation of the hardcoded public key:

The encrypted file has the following structure:

Encrypted content of the file | symmetric key | local public/private key pair | 16-byte authentication tag (Figure 14), where symmetric key, local public/private key pair comprise of 553 bytes in total.

The hexadecimal representation of 553 bytes written to the end of the file:

To decrypt the file, the victim would need to perform the following steps:

• Import the global NTRU private key into memory.
• Use the global private key to decrypt the configuration part from the encrypted file.
• Extract the local NTRU private key from the configuration file.
• Use the local private key to decrypt the symmetric key from the encrypted file.
• Use the symmetric key to decrypt the encrypted file contents.

So, the victim would need to possess a global private key to decrypt the files and presumably only a ransomware operator would have it.

After successfully encrypting the files, the HOW_TO_RESTORE note is dropped to the Desktop. The ransomware note also contains the unique identifier. The ransomware operator uses double extortion to pressure the victims into paying the ransom, and also threatens to perform a DDoS attack and call the employees of the company (Figure 14).

Based on the contents of the ransomware note, we assess with high confidence that the threat actor compiles the ransomware binary for each victim individually based on the hardcoded string found in the note and binary.

It’s worth mentioning that on July 4, 2022, Austrian daily newspaper, Der Standard, published an article about the ransomware attack on the non-profit construction and housing cooperative “Wien-Süd” GmbH, which matches the time when the ransomware started operating as well as the ransom note found in the sample we have analyzed.

How eSentire is Responding

Our Threat Response Unit (TRU) combines threat intelligence obtained from research and security incidents to create practical outcomes for our customers. We are taking a full-scale response approach to combat modern cybersecurity threats by deploying countermeasures, such as:

• Implementing threat detections to identify malicious command execution and ensure that eSentire has visibility and detections are in place across eSentire MDR for Endpoint.

• Performing global threat hunts for indicators associated with RedAlert.

Our detection content is supported by investigation runbooks, ensuring our SOC (Security Operations Center) analysts respond rapidly to any intrusion attempts related to known malware Tactics, Techniques, and Procedures. In addition, TRU closely monitors the threat landscape and constantly addresses capability gaps and conducts retroactive threat hunts to assess customer impact.

Recommendations from eSentire's Threat Response Unit (TRU)

We recommend implementing the following controls to help secure your organization against RedAlert ransomware:

• Confirm that all devices are protected with Endpoint Detection and Response (EDR) solutions.
• Maintain the backups for Virtual Machines.
• Consider implementing the Lockdown Mode for ESXi hosts.

While the TTPs used by adversaries grow in sophistication, they lead to a certain level of difficulties at which critical business decisions must be made. Preventing the various attack paths utilized by the modern threat actor requires actively monitoring the threat landscape, developing, and deploying endpoint detection, and the ability to investigate logs & network data during active intrusions.

eSentire’s TRU is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.

If you are not currently engaged with an MDR provider, eSentire MDR can help you reclaim the advantage and put your business ahead of disruption.

Learn what it means to have an elite team of Threat Hunters and Researchers that works for you. Connect with an eSentire Security Specialist.

Appendix

• https://www.bleepingcomputer.com/news/security/new-redalert-ransomware-targets-windows-linux-vmware-esxi-servers/
• https://twitter.com/malwrhunterteam/status/1544387107577335813?s=20&t=j9ibAwJRIDYiKEPJkkLa6g
• https://id-ransomware.blogspot.com/2017/01/red-alert-ransomware.html
• https://github.com/goliate/hidden-tear
• https://en.wikipedia.org/wiki/NTRU
• https://www.esat.kuleuven.be/cosic/publications/thesis-161.pdf
• https://www.topcoder.com/blog/shors-algorithm-in-quantum-computing/#:~:text=Shor's%20algorithm%20was%20invented%20by,order%20polynomial%20in%20log%20N.
• https://www.cisa.gov/uscert/sites/default/files/publications/AR21-126A_FiveHands_Ransomware.pdf
• https://developer.vmware.com/web/tool/7.0/esxcli
• https://www.derstandard.at/story/2000137275833/hackerangriff-auf-wohngenossenschaft-wien-sued
• https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.security.doc/GUID-88B24613-E8F9-40D2-B838-225F5FF480FF.html

Indicators of Compromise

Yara Rules

rule RaccoonStealer_v2 {
   rule  RedAlert {
    meta:
        author = "eSentire TI"
        date = "07/18/2022"
    strings:
        $file_enc1 = ".log"
        $file_enc2 = ".vmdk" 
        $encryption = "ntru_encrypt"
        $enc_extension = ".crypt658"  
        $ransom_note = "HOW_TO_RESTORE"
    condition:
        uint32(0) == 0x464c457f
        and filesize < 500KB
        and all of them
}