AA21-265A: Conti Ransomware

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Original release date: September 22, 2021

Summary

Immediate Actions You Can Take Now to Protect Against Conti Ransomware
• Use multi-factor authentication.
• Segment and segregate networks and functions.
• Update your operating system and software.

Note: This Alert uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework, version 9. See the ATT&CK for Enterprise for all referenced threat actor tactics and techniques.

The Cybersecurity and Infrastructure Security Agency (CISA) and the Federal Bureau of Investigation (FBI) have observed the increased use of Conti ransomware in more than 400 attacks on U.S. and international organizations. In typical Conti ransomware attacks, malicious cyber actors steal files, encrypt servers and workstations, and demand a ransom payment. 

To secure systems against Conti ransomware, CISA, FBI, and the National Security Agency (NSA) recommend implementing the mitigation measures described in this Advisory, which include requiring multi-factor authentication (MFA), implementing network segmentation, and keeping operating systems and software up to date.

Click here for a PDF version of this report.

Click here for indicators of compromise (IOCs) in STIX format.

Technical Details

While Conti is considered a ransomware-as-a-service (RaaS) model ransomware variant, there is variation in its structure that differentiates it from a typical affiliate model. It is likely that Conti developers pay the deployers of the ransomware a wage rather than a percentage of the proceeds used by affiliate cyber actors and receives a share of the proceeds from a successful attack. 

Conti actors often gain initial access [TA0001] to networks through:

  • Spearphishing campaigns using tailored emails that contain malicious attachments [T1566.001] or malicious links [T1566.002];
    • Malicious Word attachments often contain embedded scripts that can be used to download or drop other malware—such as TrickBot and IcedID, and/or Cobalt Strike—to assist with lateral movement and later stages of the attack life cycle with the eventual goal of deploying Conti ransomware. [1],[2],[3]
  • Stolen or weak Remote Desktop Protocol (RDP) credentials [T1078].[4]
  • Phone calls;
  • Fake software promoted via search engine optimization;
  • Other malware distribution networks (e.g., ZLoader); and
  • Common vulnerabilities in external assets.

In the execution phase [TA0002], actors run a getuid payload before using a more aggressive payload to reduce the risk of triggering antivirus engines. CISA and FBI have observed Conti actors using Router Scan, a penetration testing tool, to maliciously scan for and brute force [T1110] routers, cameras, and network-attached storage devices with web interfaces. Additionally, actors use Kerberos attacks [T1558.003] to attempt to get the Admin hash to conduct brute force attacks.

Conti actors are known to exploit legitimate remote monitoring and management software and remote desktop software as backdoors to maintain persistence [TA0003] on victim networks.[5] The actors use tools already available on the victim network—and, as needed, add additional tools, such as Windows Sysinternals and Mimikatz—to obtain users’ hashes and clear-text credentials, which enable the actors to escalate privileges [TA0004] within a domain and perform other post-exploitation and lateral movement tasks [TA0008]. In some cases, the actors also use TrickBot malware to carry out post-exploitation tasks.

According to a recently leaked threat actor “playbook,” [6] Conti actors also exploit vulnerabilities in unpatched assets, such as the following, to escalate privileges [TA0004] and move laterally [TA0008] across a victim’s network:

  • 2017 Microsoft Windows Server Message Block 1.0 server vulnerabilities; [7]
  • “PrintNightmare” vulnerability (CVE-2021-34527) in Windows Print spooler [8] service; and
  • “Zerologon” vulnerability (CVE-2020-1472) in Microsoft Active Directory Domain Controller systems.[9]

Artifacts leaked with the playbook identify four Cobalt Strike server Internet Protocol (IP) addresses Conti actors previously used to communicate with their command and control (C2) server.

  • 162.244.80[.]235
  • 85.93.88[.]165
  • 185.141.63[.]120
  • 82.118.21[.]1

CISA and FBI have observed Conti actors using different Cobalt Strike server IP addresses unique to different victims.

Conti actors often use the open-source Rclone command line program for data exfiltration [TA0010]. After the actors steal and encrypt the victim’s sensitive data [T1486], they employ a double extortion technique in which they demand the victim pay a ransom for the release of the encrypted data and threaten the victim with public release of the data if the ransom is not paid.

MITRE ATT&CK Techniques

Conti ransomware uses the ATT&CK techniques listed in table 1.

Table 1: Conti ATT&CK techniques for enterprise
Initial Access
Technique Title ID Use
Valid Accounts T1078 Conti actors have been observed gaining unauthorized access to victim networks through stolen Remote Desktop Protocol (RDP) credentials. 
Phishing: Spearphishing Attachment  T1566.001 Conti ransomware can be delivered using TrickBot malware, which is known to use an email with an Excel sheet containing a malicious macro to deploy the malware.
Phishing: Spearphishing Link  T1566.002 Conti ransomware can be delivered using TrickBot, which has been delivered via malicious links in phishing emails.
Execution
Technique Title ID Use
Command and Scripting Interpreter: Windows Command Shell  T1059.003 Conti ransomware can utilize command line options to allow an attacker control over how it scans and encrypts files.
Native Application Programming Interface (API)  T1106 Conti ransomware has used API calls during execution.
Persistence
Technique Title ID Use
Valid Accounts T1078 Conti actors have been observed gaining unauthorized access to victim networks through stolen RDP credentials. 
External Remote Services T1133 Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as virtual private networks (VPNs), Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services. Services such as Windows Remote Management can also be used externally.
Privilege Escalation
Technique Title ID Use
Process Injection: Dynamic-link Library Injection T1055.001 Conti ransomware has loaded an encrypted dynamic-link library (DLL) into memory and then executes it. 
Defense Evasion
Technique Title ID Use
Obfuscated Files or Information  T1027 Conti ransomware has encrypted DLLs and used obfuscation to hide Windows API calls.
Process Injection: Dynamic-link Library Injection T1055.001 Conti ransomware has loaded an encrypted DLL into memory and then executes it.
Deobfuscate/Decode Files or Information  T1140 Conti ransomware has decrypted its payload using a hardcoded AES-256 key.
Credential Access
Technique Title ID Use
Brute Force T1110 Conti actors use legitimate tools to maliciously scan for and brute force routers, cameras, and network-attached storage devices with web interfaces.
Steal or Forge Kerberos Tickets: Kerberoasting T1558.003 Conti actors use Kerberos attacks to attempt to get the Admin hash.
System Network Configuration Discovery  T1016 Conti ransomware can retrieve the ARP cache from the local system by using the GetIpNetTable() API call and check to ensure IP addresses it connects to are for local, non-internet systems.
System Network Connections Discovery  T1049 Conti ransomware can enumerate routine network connections from a compromised host.
Process Discovery T1057 Conti ransomware can enumerate through all open processes to search for any that have the string sql in their process name.
File and Directory Discovery  T1083 Conti ransomware can discover files on a local system.
Network Share Discovery T1135 Conti ransomware can enumerate remote open server message block (SMB) network shares using NetShareEnum().
Lateral Movement
Technique Title ID Use
Remote Services: SMB/Windows Admin Shares  T1021.002 Conti ransomware can spread via SMB and encrypts files on different hosts, potentially compromising an entire network.
Taint Shared Content T1080 Conti ransomware can spread itself by infecting other remote machines via network shared drives.
Impact
Technique Title ID Use
Data Encrypted for Impact T1486 Conti ransomware can use CreateIoCompletionPort(), PostQueuedCompletionStatus(), and GetQueuedCompletionPort() to rapidly encrypt files, excluding those with the extensions of .exe, .dll, and .lnk. It has used a different AES-256 encryption key per file with a bundled RAS-4096 public encryption key that is unique for each victim. Conti ransomware can use “Windows Restart Manager” to ensure files are unlocked and open for encryption.
Service Stop T1489 Conti ransomware can stop up to 146 Windows services related to security, backup, database, and email solutions through the use of net stop.
Inhibit System Recovery T1490 Conti ransomware can delete Windows Volume Shadow Copies using vssadmin.

Mitigations

CISA, FBI, and NSA recommend that network defenders apply the following mitigations to reduce the risk of compromise by Conti ransomware attacks.

Use multi-factor authentication.

Implement network segmentation and filter traffic.

  • Implement and ensure robust network segmentation between networks and functions to reduce the spread of the ransomware. Define a demilitarized zone that eliminates unregulated communication between networks.
  • Filter network traffic to prohibit ingress and egress communications with known malicious IP addresses. 
  • Enable strong spam filters to prevent phishing emails from reaching end users. Implement a user training program to discourage users from visiting malicious websites or opening malicious attachments. Filter emails containing executable files to prevent them from reaching end users.
  • Implement a URL blocklist and/or allowlist to prevent users from accessing malicious websites.

Scan for vulnerabilities and keep software updated. 

  • Set antivirus/antimalware programs to conduct regular scans of network assets using up-to-date signatures. 
  • Upgrade software and operating systems, applications, and firmware on network assets in a timely manner. Consider using a centralized patch management system. 

Remove unnecessary applications and apply controls.

  • Remove any application not deemed necessary for day-to-day operations. Conti threat actors leverage legitimate applications—such as remote monitoring and management software and remote desktop software applications—to aid in the malicious exploitation of an organization’s enterprise. 
  • Investigate any unauthorized software, particularly remote desktop or remote monitoring and management software.
  • Implement application allowlisting, which only allows systems to execute programs known and permitted by the organization’s security policy. Implement software restriction policies (SRPs) or other controls to prevent programs from executing from common ransomware locations, such as temporary folders supporting popular internet browsers or compression/decompression programs.
  • Implement execution prevention by disabling macro scripts from Microsoft Office files transmitted via email. Consider using Office Viewer software to open Microsoft Office files transmitted via email instead of full Microsoft Office suite applications.
  • See the joint Alert, Publicly Available Tools Seen in Cyber Incidents Worldwide—developed by CISA and the cybersecurity authorities of Australia, Canada, New Zealand, and the United Kingdom—for guidance on detection and protection against malicious use of publicly available tools.

Implement endpoint and detection response tools. 

  • Endpoint and detection response tools allow a high degree of visibility into the security status of endpoints and can help effectively protect against malicious cyber actors. 

Limit access to resources over the network, especially by restricting RDP. 

  • After assessing risks, if RDP is deemed operationally necessary, restrict the originating sources and require multi-factor authentication.

Secure user accounts.

  • Regularly audit administrative user accounts and configure access controls under the principles of least privilege and separation of duties.
  • Regularly audit logs to ensure new accounts are legitimate users.

Review CISA’s APTs Targeting IT Service Provider Customers guidance for additional mitigations specific to IT Service Providers and their customers.

Use the Ransomware Response Checklist in case of infection.

If a ransomware incident occurs at your organization, CISA, FBI, and NSA recommend the following actions:

CISA, FBI, and NSA strongly discourage paying a ransom to criminal actors. Paying a ransom may embolden adversaries to target additional organizations, encourage other criminal actors to engage in the distribution of ransomware, and/or may fund illicit activities. Paying the ransom also does not guarantee that a victim’s files will be recovered.

Additional Resources

Free Cyber Hygiene Services

CISA offers a range of no-cost cyber hygiene services to help organizations assess, identify, and reduce their exposure to threats, including ransomware. By requesting these services, organizations of any size could find ways to reduce their risk and mitigate attack vectors.

StopRansomware.gov 

The StopRansomware.gov webpage is an interagency resource that provides guidance on ransomware protection, detection, and response. This includes ransomware alerts, reports, and resources from CISA and other federal partners, including:

Rewards for Justice Reporting

The U.S. Department of State’s Rewards for Justice (RFJ) program offers a reward of up to $10 million for reports of foreign government malicious activity against U.S. critical infrastructure. See the RFJ website for more information and how to report information securely.

Contact Information

To report suspicious or criminal activity related to information found in this Joint Cybersecurity Advisory, contact your local FBI field office at www.fbi.gov/contact-us/field-offices, or the FBI’s 24/7 Cyber Watch (CyWatch) at (855) 292-3937 or by e-mail at CyWatch@fbi.gov. When available, please include the following information regarding the incident: date, time, and location of the incident; type of activity; number of people affected; type of equipment used for the activity; the name of the submitting company or organization; and a designated point of contact. If you have any further questions related to this Joint Cybersecurity Advisory, or to request incident response resources or technical assistance related to these threats, contact CISA at CISAServiceDesk@cisa.dhs.gov. For NSA client requirements or general cybersecurity inquiries, contact the NSA Cybersecurity Requirements Center at 410-854-4200 or Cybersecurity_Requests@nsa.gov.

References

Revisions

  • September 22, 2021: Initial Version

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