Egregor – Prolock: Fraternal Twins ? | Cybersécurité

CERT Intrinsec has faced since the beginning of September several cases involving Egregor and Prolock ransomwares. This article aims at presenting Egregor and Prolock techniques, tactics and procedures, as well as sharing indicators of compromise and highlighting actions of the threat actor operating both ransomwares, according to collected intelligence and TTPs analysis.

On one hand, Egregor has a similar strategy to other ransomwares, as it exfiltrates data, encrypts files and publishes them on its website in order to make victims pay the ransom. It is active since the beginning of September 2020 and impacts many sectors from insurance to transport. Its goal is lucrative.

On the other hand, Prolock, successor of PwndLocker, is active since March 2020. As many other ransomwares, it targets big companies with ransoms going from 35 to 255 bitcoins (400 000 to 3 000 000 $). Its goal is, as far as we know, only lucrative. Prolock is active mainly in Northern America and in Europe and impacts several sectors, such as health, construction, finance, legal, etc.

Kill chain

Egregor ransomware analysis

Initial access

We were not able to find identified specific initial accesses, we found traces of Qakbot during investigations but we could not identify how it was dropped on information systems. We observed many potential intrusion vectors on patient 0 (many malwares were found on the machine).

Internal reconnaissance

Prior to privilege escalation, Egregor proceeds to Active Directory reconnaissance using tools such as Sharphound or AdFind. These tools are used to gather information about users, groups, computers, and so on. They aim as well at finding the best compromission paths.

Privilege escalation

During investigations, Egregor compromises Active Directory in order to become domain admin.

Lateral movement

Egregor moves laterally on information systems using CobaltStrike SMB beacons. This feature allows an attacker to use SMB named pipes (logical connections between a client and a server) to communicate commands through the information system revealing C2 IP address.

The following command line is a service created by CobaltStrike and can be found in Windows Event Logs (event id 7045). It runs an encoded powershell command.

Svg%3ECobaltStrike service execution

It is possible to deobfuscate CobaltStrike payloads (base64, gunzip and XOR operations) using CyberChef[1]:

Svg%3ECobaltStrike payload deobfuscation

C2 Communication

Once settles on victim’s information systems, Egregor communicates with its Command and Control servers via HTTPS protocol so as to drop scripts or dynamic link libraries on infected hosts. You can find the list of C2 identified during investigations in section “IP Addresses”.

Data exfiltration

Egregor masquerades svchost.exe process to launch an RClone client in order to exfiltrate data. RClone aims at managing files in cloud, it deals with multiple systems and protocols. The RClone configuration file, in plain text, is dropped by the attacker with the binary. Based on investigations and OSINT, we know that Egregor used at least three different configurations to exfiltrate data.

Svg%3ERClone Configuration File (WebDav)

Svg%3ERClone Configuration File (sFTP)

Svg%3ERClone Configuration File (DropBox)

Defense evasion

To evade protections, Egregor create a Group Policy Object to disable Windows Defender and try to takedown any anti-virus console prior to ransomware execution:

Display name: New Group Policy Object
Version: 1
registry.pol content:
– Key path: SoftwarePoliciesMicrosoftWindows Defender
– Data name: DisableAntiSpyware
– Value type: 0x04 (REG_DWORD)
– Data value: 0x01

Ransomware execution

Egregor downloads custom dynamic link libraries (b.dll, q.dll, etc) using bitsadmin and execute them on victim’s systems to encrypt data.

Svg%3EDLL download and execution

Prolock ransomware analysis

Initial Access

One of the intrusion vectors is malspam. Indeed, Emotet is used to initiate infection on several user workstations and to drop Qakbot. Emotet used legitimate documents after taking control of some user’s email accounts. These documents contain a payload which tries to download a binary file from different URLs, as following. On infected systems, after the execution of the binary retrieved by Emotet code, few files are created (typical Qakbot operation):

  • AppDataRoamingMicrosoftJfayaevatgrcxt.exe
  • koyxogldypnalvvlyxpw.exe
  • AdFind.exe

Svg%3ECode embedded in the malicious document

Svg%3EPowershell payload (decoded from base64)

Svg%3EDeobfuscated powershell code (used to download F889k6.exe)

Unfortunately, we were not able to retrieve F889k6.exe neither from compromised systems nor from URLs, which were already down by that time.

Internal reconnaissance

Prolock proceeds to Active Directory reconnaissance AdFind tool to gather information about users, groups, computers so as to prepare exfiltration and ransomware execution.

Privilege escalation

During investigations, Prolock compromises Active Directory in order to become domain admin.

Lateral movement

Prolock uses batch scripts to enable RDP on targeted hosts. We found the script below during one of our cases. The same script has already be found on Prolock cases.

Following actions are performed by the script:

  • Enable Remote Desktop connections by setting fDenyConnections to 0.
  • Start Microsoft Protection Service.
  • Set a rule in Windows firewall to activate RDP service.
  • Modify RDP-Tcp registry key.

Svg%3Erdp.bat script (enable RDP connections)

Data exfiltration

We did not see any use of RClone during incident responses involving Prolock.

Ransomware execution

Prolock uses different scripts and files to encrypt victim’s data. It retrieves all these files from 185.238.0[.]233, the latter hosting as well Egregor dynamic link libraries. The first script wmi_md.bat (wmi_u.bat works the same way) proceeds the following actions on each host whose IP address is in the file list_md.txt (or list_u.txt):

  • Connect to the host using a compromised account
  • Drop connect.bat and office.txt on the host
  • Execute connect.bat using WMI command-line
  • Write host IP address in log.dat file
  • Cancel the network connection

Svg%3EScript deploying ransomware on information system (wmi_md.bat)

In addition, we found a script that uses bitsadmin to download office.txt and connect.bat from 185.238.0[.]233.

Svg%3ECode from eb1.bat

The script connect.bat contains the following encoded powershell payload.

Svg%3EPowershell payload from connect.bat

After decoding and deobfuscating it, we got to know that it is used to load office.txt in memory and execute it.

Svg%3EDecoded and deobfuscated payload

Office.txt analysis is not yet complete, but we believe that it is the ransomware, based on system events correlation.

Relations between Egregor & Prolock

During recent investigations, we observed common indicators of compromise and techniques between Egregor and Prolock. These common points are presented below:

  • The IP address 185.238.0[.]233 hosts both Egregor’s dynamic link libraries and Prolock files (especially scripts used to run the ransomware). You can find more information about Prolock TTP in the next section.
  • Both WIN-799RI0TSTOF and WIN-4K804V6ADVQ hostnames of potential VPS have been seen during Prolock and Egregor cases.
  • list_md.txt and list_u.txt files were involved in both Egregor and Prolock cases (of course, their content depends on the victim’s information system).
  • The use of bitsadmin in eb*.bat scripts to download dll (Egregor) or scripts (Prolock) is another common point between these threat actors.
  • md.exe binary has been seen on both Egregor and Prolock cases.
  • Even if we did not notice exfiltration using RClone in our Prolock cases, we know that this threat actor uses it[2].

Svg%3ETimeline of incident responses involving Prolock and Egregor insisting on common indicators of compromise

Indicators of compromise

Incident response

Binaries
File Size (bytes) MD5 SHA1 SHA256
md.exe 4516928 4183104 5ed9fb5fc74c6fdb3537629e9b23437a
N/A
67424175620be87fd3b2810ba5eba0d9e0bee49f
7e0018e18f6bd230366a2b6f031c52ee8899f8dc
fec51f04710e3aae47dd23b084d8a364fa07c25dda5b229aeb3e6a98c56fa869
N/A
svchost.exe 42043904 4a97c4345aabf9dd922d29687c95ac66 f54bf6a4c6f7c3d0077d152a094e3c7738cf0bd1 5bc506b9f61ecec47326892dfd17d958d3568b189dca3afd09f6daffa021acc0
main_target1.exe 4516416 a3e1ea9438e293ec8fae62c39ea3f0e4 e9581cb5161f10f5e99e0cb6c30c201e6e844676 089bb9d18b3faf4618c50f553e85ae47256b948af9ab5b91a802204510ec618f
b.dll 808960 a654b3a37c27810db180822b72ad6d3e d2d9484276a208641517a2273d96f34de1394b8e 4c9e3ffda0e663217638e6192a093bbc23cd9ebfbdf6d2fc683f331beaee0321
q.dll 784896 520ee511034717f5499fb66f9c0b76a5 3a33de9a84bbc76161895178e3d13bcd28f7d8fe a5989c480ec6506247325652a1f3cb415934675de3877270ae0f65edd9b14d13
qymrkrr.exe N/A N/A N/A N/A
fxmgwk.exe N/A N/A N/A N/A
cthwiilhz.exe N/A N/A N/A N/A
erkftj.exe N/A N/A N/A N/A
c6d7790.exe N/A N/A N/A N/A
c6d7790.exe N/A N/A N/A N/A
a31b29b.exe N/A N/A N/A N/A
ed53e67.exe N/A N/A N/A N/A
3f2eb85.exe N/A N/A N/A N/A
Scripts
File Size (bytes) MD5 SHA1 SHA256
e.bat 156
157
7375083934dd17f0532da3bd6770ab25 N/A ac6d919b313bbb18624d26745121fca3e4ae0fd3 1be22505a25f14fff1e116fafcaae9452be325b1 f0adfd3f89c9268953f93bfdfefb84432532a1e30542fee7bddda14dcb69a76c N/A
eb.bat 58 N/A 9dacb159779d5e57798632bac74ae5b880cf1ec8 N/A
eb1.bat 253 3872e7caaede9ee1ce8f37435dcaf836 8f166dfeb2fd8780de0e3dbdb25d0fdb373f58de c9df055f380100a7301f5252c5fc03bb1de06cc46fe32f85345ff60a78d12453
connect.bat 7004 6cebf3c01844520e8b27023d8f47a0ed f5b14cc494303c91456bb50e7816358b6766a5b8 bd1dba49596c04677a2aa2bf53193d5b08d2b41ad2e377f1d0ecb8de8d25876e
wmi_u.bat 421 9deca294973f6d52f9506240b104079c f098e6931eb32f9d28f681ad6fd2716a65b7f140 87a699923f3edeb6ce631f9bf985286acf3f1794b4bb3d14ea36b270d8d2d33b
wmi_md.bat 416 463d45502447c7aa58538159eccc1a1a 4bad78fccfc69f4f9ac619dd9a8a9f70c3cc3ed0 a9d3c1d779550b003128583cbe8c2a363db5ad99ecb5a2896cc9f38464659bfc
rdp.bat 329 dc1aafc01b5068eef6c2ed4cfd6864ed eb43350337138f2a77593c79cee1439217d02957 ac49c114ef137cc198786ad8daefa9cfcc01f0c0a827b0e2b927a7edd0fca8b0
Other files
File Size (bytes) SHA1
svchost.conf 155 bae4323aa7fa3e4de9ab021d72ecd84de795351b
office.txt 30608 4769a775fd4a2c29b433736a59dc4277354a54f2
list_u.txt 4560 9269 3b59fdff922497dc24d7cec0b219e93334e81221 33c776f25ed3bb6011bfe96c13467815fb993289
list_md.txt 4773 9633 1a3c149a2720f001a0a475ae978114090f3ed720 aaf4374400c63b0dae41f67bd90cd2ebb2c159db
list3.txt 4560 3b59fdff922497dc24d7cec0b219e93334e81221
[HOW TO RECOVER FILES].TXT 1085 620311402640b1547d59722b63f19fab082a57af
RECOVER-FILES.txt N/A N/A
C2 Domain names
  • amajai-technologies[.]network
  • amajai-technologies[.]industries
IP adresses
  • IP addresses hosting dll and scripts:
  • Server using for potential data exfiltration
  • IP addresses communicating with infected systems through CobaltStrike
  • Potential VPS IP addresses
Potential VPS Hostnames
  • WIN-799RI0TSTOF
  • WIN-4K804V6ADVQ
  • DESKTOP-LHC2KTF
  • DESKTOP-93VHU8M

Threat Intelligence

Using IOC collected during incident responses, we hunted some other Egregor files, especially from 185.238.0[.]233. We found similar dynamic link libraries (a.dll, p.dll, etc), as well as the RClone configuration file we presented in section “Data Exfiltration“.

Svg%3E

File Size (bytes) SHA1
b.dll 808960 d2d9484276a208641517a2273d96f34de1394b8e
hnt.dll 498688 38c88de0ece0451b0665f3616c02c2bad77a92a2
kk.dll 498176 09d8c91ccefd699fb5ac1aaebeeebee25170fe1a
p.dll 784896 8768cf56e12a81d838e270dca9b82d30c35d026e
p.dll 500224 fafd32e972ebb33b187bfb1ebf1a6ecb1d2d7239
sed.dll 806400 b7170443ea2b73bca3d16958712ee57cb4869d5b
  • CobaltStrike C2 Domain names[3]
  • atakai-technologies[.]space
  • atakai-technologies[.]website
  • atakai-technologies[.]host
  • atakai-technologies[.]online
  • atakai-technologies[.]work
  • akamai-technologies[.]host
  • akamai-technologies[.]site
  • akamai-technologies[.]space
  • akamai-technologies[.]digital
  • akamai-technologies[.]website
  • akamai-technologies[.]online
  • amajai-technologies[.]host
  • amajai-technologies[.]website
  • amajai-technologies[.]network
  • amajai-technologies[.]digital
  • amajai-technologies[.]space
  • amajai-technologies[.]tech
  • amajai-technologies[.]industries
  • amamai-tecnologies[.]space
  • amamai-tecnologies[.]cloud
  • amamai-tecnologies[.]digital
  • amatai-technologies[.]website
  • amatai-technologies[.]digital
  • amatai-technologies[.]space
  • amatai-technologies[.]site

MITRE ATT&CK

Prolock

Tactic Technique
Initial Access Phishing (T1566): Spearphishing attachment (T1566.001)
Execution User Execution (T1204): Malicious File (T1204.002) Windows Management Instrumentation (T1047)
Persistence Scheduled Task/Job (T1053): Scheduled Task (T1053.005) Valid Accounts (T1078)
Discovery Account Discovery (T1087) Domain Trust Discovery (T1482) Permission Groups Discovery (T1069): Domain Groups (T1069.001)
Lateral Movement Remote Services (T1021): Remote Desktop Protocol (T1021.001) Valid Accounts (T1078)
Command and Control Ingress Tool Transfert (T1105)
Impact Data encrypted for impact (T1486)

Egregor

Tactic Technique
Execution Scheduled Task/Job (T1053): Scheduled Task (T1053.005) Services Execution (T1569): Service Execution (T1569.002) Windows Management Instrumentation (T1047)
Persistence Create or modify system process (T1543): Windows Service (T1543.003)
Defense Evasion Impair Defenses (T1562): Disable or modify tools (T1562.001)
Discovery Account Discovery (T1087) Domain Trust Discovery (T1482) Permission Groups Discovery (T1069): Domain Groups (T1069.001)
Lateral Movement Remote Services (T1021): SMB/Windows Admin Shares (T1021.002)
Command and Control Application Layer Protocol (T1071)
Exfiltration Exfiltration over web service (T1567): Exfiltration to Cloud Storage (T1567.002)
Impact Data encrypted for impact (T1486)

References

CyberChef recipe to deobfuscate CobaltStrike payloads : [1] https://github.com/mattnotmax/cyberchef-recipes#recipe-28—de-obfuscation-of-cobalt-strike-beacon-using-conditional-jumps-to-obtain-shellcode

Article from Group-IB about Prolock : [2]https://www.group-ib.com/blog/prolock

CobaltStrike C2 List : [3]https://twitter.com/smoothimpact/status/1308033998371905538