Iranian Cyber Actors’ Brute Force and Credential Access Activity Compromises Critical Infrastructure Organizations

Summary

The Federal Bureau of Investigation (FBI), the Cybersecurity and Infrastructure Security Agency (CISA), the National Security Agency (NSA), the Communications Security Establishment Canada (CSE), the Australian Federal Police (AFP), and Australian Signals Directorate’s Australian Cyber Security Centre (ASD’s ACSC) are releasing this joint Cybersecurity Advisory to warn network defenders of Iranian cyber actors’ use of brute force and other techniques to compromise organizations across multiple critical infrastructure sectors, including the healthcare and public health (HPH), government, information technology, engineering, and energy sectors. The actors likely aim to obtain credentials and information describing the victim’s network that can then be sold to enable access to cybercriminals.

Since October 2023, Iranian actors have used brute force, such as password spraying, and multifactor authentication (MFA) ‘push bombing’ to compromise user accounts and obtain access to organizations. The actors frequently modified MFA registrations, enabling persistent access. The actors performed discovery on the compromised networks to obtain additional credentials and identify other information that could be used to gain additional points of access. The authoring agencies assess the Iranian actors sell this information on cybercriminal forums to actors who may use the information to conduct additional malicious activity.

This advisory provides the actors’ tactics, techniques, and procedures (TTPs) and indicators of compromise (IOCs). The information is derived from FBI engagements with entities impacted by this malicious activity.

The authoring agencies recommend critical infrastructure organizations follow the guidance provided in the Mitigations section. At a minimum, organizations should ensure all accounts use strong passwords and register a second form of authentication.

Download the PDF version of this report:

For a downloadable list of IOCs, see:

Technical Details

Note: This advisory uses the MITRE ATT&CK^® for Enterprise framework, version 15. See the MITRE ATT&CK Tactics and Techniques section in Appendix A for a table of the actors’ activity mapped to MITRE ATT&CK tactics and techniques.

Overview of Activity

The actors likely conduct reconnaissance operations to gather victim identity [T1589] information. Once obtained, the actors gain persistent access to victim networks frequently via brute force [T1110]. After gaining access, the actors use a variety of techniques to further gather credentials, escalate privileges, and gain information about the entity’s systems and network. The actors also move laterally and download information that could assist other actors with access and exploitation.

Initial Access and Persistence

The actors use valid user and group email accounts [T1078], frequently obtained via brute force such as password spraying [T1110.003] although other times via unknown methods, to obtain initial access to Microsoft 365, Azure [T1078.004], and Citrix systems [T1133]. In some cases where push notification-based MFA was enabled, the actors send MFA requests to legitimate users seeking acceptance of the request. This technique—bombarding users with mobile phone push notifications until the user either approves the request by accident or stops the notifications— is known as “MFA fatigue” or “push bombing” [T1621].

Once the threat actors gain access to an account, they frequently register their devices with MFA to protect their access to the environment via the valid account:

• In two confirmed compromises, the actors leveraged a compromised user’s open registration for MFA [T1556.006] to register the actor’s own device [T1098.005] to access the environment.
• In another confirmed compromise, the actors used a self-service password reset (SSPR) tool associated with a public facing Active Directory Federation Service (ADFS) to reset the accounts with expired passwords [T1484.002] and then registered MFA through Okta for compromised accounts without MFA already enabled [T1556] [T1556.006].

The actors frequently conduct their activity using a virtual private network (VPN) service [T1572]. Several of the IP addresses in the actors’ malicious activity originate from exit nodes tied to the Private Internet Access VPN service.

Lateral Movement

The actors use Remote Desktop Protocol (RDP) for lateral movement [T1021.001]. In one instance, the actors used Microsoft Word to open PowerShell to launch the RDP binary mstsc.exe [T1202].

Credential Access

The actors likely use open-source tools and methodologies to gather more credentials. The actors performed Kerberos Service Principal Name (SPN) enumeration of several service accounts and received Kerberos tickets [T1558.003]. In one instance, the actors used the Active Directory (AD) Microsoft Graph Application Program Interface (API) PowerShell application likely to perform a directory dump of all AD accounts. Also, the actors imported the tool [T1105] DomainPasswordSpray.ps1, which is openly available on GitHub [T1588.002], likely to conduct password spraying. The actors also used the command Cmdkey /list, likely to display usernames and credentials [T1555].

Privilege Escalation

In one instance, the actors attempted impersonation of the domain controller, likely by exploiting Microsoft’s Netlogon (also known as ”Zerologon”) privilege escalation vulnerability (CVE-2020-1472) [T1068].

Discovery

The actors leverage living off the land (LOTL) to gain knowledge about the target systems and internal networks. The actors used the following Windows command-line tools to gather information about domain controllers [T1018], trusted domains [T1482], lists of domain administrators, and enterprise administrators [T1087.002] [T1069.002] [T1069.003]:

• Nltest /dclist
• Nltest /domain_trusts
• Nltest /domain_trusts/all_trusts
• Net group “Enterprise admins” /domain
• Net group “Domain admins” /domain

Next, the actors used the following Lightweight Directory Access Protocol (LDAP) query in PowerShell [T1059.001]to search the AD for computer display names, operating systems, descriptions, and distinguished names [T1082].

                                           $i=0
                                           $D= [System.DirectoryServices.ActiveDirectory.Domain]::GetCurrentDomain()
                                           $L='LDAP://' . $D
                                           $D = [ADSI]$L
                                           $Date = $((Get-Date).AddDays(-90).ToFileTime())
                                           $str = '(&(objectcategory=computer)(operatingSystem=*serv*)(|(lastlogon>='+$Date+')(lastlogontimestamp>='+$Date+')))'
                                           $s = [adsisearcher]$str
                                           $s.searchRoot = $L.$D.distinguishedName
                                           $s.PropertiesToLoad.Add('cn') > $Null
                                           $s.PropertiesToLoad.Add('operatingsystem') > $Null
                                           $s.PropertiesToLoad.Add('description') > $Null
                                           $s.PropertiesToLoad.Add('distinguishedName') > $Null
                                           Foreach ($CA in $s.FindAll()) {
                                                         Write-Host $CA.Properties.Item('cn')
                                                         $CA.Properties.Item('operatingsystem')
                                                         $CA. Properties.Item('description')
                                                         $CA.Properties.Item('distinguishedName')
                                                         $i++
                                           }
                                           Write-host Total servers: $i

Command and Control

On one occasion, using msedge.exe, the actors likely made outbound connections to Cobalt Strike Beacon command and control (C2) infrastructure [T1071.001].

Exfiltration and Collection

In a couple instances, while logged in to victim accounts, the actors downloaded files related to gaining remote access to the organization and to the organization’s inventory [T1005], likely exfiltrating the files to further persist in the victim network or to sell the information online.

Detection

To detect brute force activity, the authoring agencies recommend reviewing authentication logs for system and application login failures of valid accounts and looking for multiple, failed authentication attempts across all accounts.

To detect the use of compromised credentials in combination with virtual infrastructure, the authoring agencies recommend the following steps:

• Look for “impossible logins,” such as suspicious logins with changing usernames, user agent strings, and IP address combinations or logins where IP addresses do not align to the user’s expected geographic location.
• Look for one IP used for multiple accounts, excluding expected logins.
• Look for “impossible travel.” Impossible travel occurs when a user logs in from multiple IP addresses with significant geographic distance (i.e., a person could not realistically travel between the geographic locations of the two IP addresses during the period between the logins). Note: Implementing this detection opportunity can result in false positives if legitimate users apply VPN solutions before connecting into networks.
• Look for MFA registrations with MFA in unexpected locales or from unfamiliar devices.
• Look for processes and program execution command-line arguments that may indicate credential dumping, especially attempts to access or copy the ntds.dit file from a domain controller.
• Look for suspicious privileged account use after resetting passwords or applying user account mitigations.
• Look for unusual activity in typically dormant accounts.
• Look for unusual user agent strings, such as strings not typically associated with normal user activity, which may indicate bot activity.

Mitigations

The authoring agencies recommend organizations implement the mitigations below to improve organizations’ cybersecurity posture based on the actors’ TTPs described in this advisory. These mitigations align with the Cross-Sector Cybersecurity Performance Goals (CPGs) developed by CISA. The CPGs, which are organized to align to the National Institute of Standards and Technology (NIST) Cybersecurity Framework, are a subset of cybersecurity practices, aimed at meaningfully reducing risks to both critical infrastructure operations and the American people. These voluntary CPGs strive to help small- and medium-sized organizations kick-start their cybersecurity efforts by prioritizing investment in a limited number of essential actions with high-impact security outcomes. Visit CISA’s Cross-Sector Cybersecurity Performance Goals for more information on the CPGs, including additional recommended baseline protections.

• Review IT helpdesk password management related to initial passwords, password resets for user lockouts, and shared accounts. IT helpdesk password procedures may not align to company policy for user verification or password strength, creating a security gap. Avoid common passwords (e.g. “Spring2024” or “Password123!”).
• Disable user accounts and access to organizational resources for departing staff [CPG 2.D]. Disabling accounts can minimize system exposure, removing options actors can leverage for entry into the system. Similarly, create new user accounts as close as possible to an employee’s start date.
• Implement phishing-resistant MFA [CPG 2.H]. See CISA’s resources Phishing-Resistant Multifactor Authentication and More than a Password for additional information on strengthening user credentials.
• Continuously review MFA settings to ensure coverage over all active, internet-facing protocols to ensure no exploitable services are exposed [CPG 2.W].
• Provide basic cybersecurity training to users [CPG 2.I] covering concepts such as:
  • Detecting unsuccessful login attempts [CPG 2.G].
  • Having users deny MFA requests they have not generated.
  • Ensuring users with MFA-enabled accounts have MFA set up appropriately.
• Ensure password policies align with the latest NIST Digital Identity Guidelines.
  • Meeting the minimum password strength [CPG 2.B] by creating a password using 8-64 nonstandard characters and long passphrases, when possible.
• Disable the use of RC4 for Kerberos authentication.

These mitigations apply to critical infrastructure entities across sectors.

The authoring agencies also recommend software manufacturers incorporate secure by design principles and tactics into their software development practices to protect their customers against actors using compromised credentials, thereby strengthening the security posture of their customers.  For more information on secure by design, see CISA’s Secure by Design webpage and joint guide.

Validate Security Controls

In addition to applying mitigations, the authoring agencies recommend exercising, testing, and validating organization security programs against the threat behaviors mapped to the MITRE ATT&CK for Enterprise framework in this advisory. The authoring agencies recommend testing your existing security controls inventory to assess how they perform against the ATT&CK techniques described in this advisory.

To get started:

1. Select an ATT&CK technique described in this advisory (see Table 1 to Table 12).
2. Align your security technologies against the technique.
3. Test your technologies against the technique.
4. Analyze your detection and prevention technologies’ performance.
5. Repeat the process for all security technologies to obtain a set of comprehensive performance data.
6. Tune your security program, including people, processes, and technologies, based on the data generated by this process.

The authoring agencies recommend continually testing your security program, at scale, in a production environment to ensure optimal performance against the MITRE ATT&CK techniques identified in this advisory.

Contact Information

Organizations are encouraged to report suspicious or criminal activity related to information in this advisory to:

• CISA via CISA’s 24/7 Operations Center [[email protected] or 1-844-Say-CISA (1-844-729-2472)] or your local FBI field office. 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.
• For NSA cybersecurity guidance inquiries, contact [email protected].

Disclaimer

The information in this report is being provided “as is” for informational purposes only. The authoring agencies do not endorse any commercial entity, product, company, or service, including any entities, products, or services linked within this document. Any reference to specific commercial entities, products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply endorsement, recommendation, or favoring by the authoring agencies.

Intrusion events connected to this Iranian group may also include a different set of cyber actors–likely the third-party actors who purchased access from the Iranian group via cybercriminal forums or other channels. As a result, some TTPs and IOCs noted in this advisory may be tied to these third-party actors, not the Iranian actors. The TTPs and IOCs are in the advisory to provide recipients the most complete picture of malicious activity that may be observed on compromised networks. However, exercise caution if formulating attribution assessments based solely on matching TTPs and IOCs.

Version History

October 16, 2024: Initial version.

Appendix A: MITRE ATT&CK Tactics and Techniques

See Tables 1–12 for all referenced actors’ tactics and techniques in this advisory. For assistance with mapping malicious cyber activity to the MITRE ATT&CK framework, see CISA and MITRE ATT&CK’s Best Practices for MITRE ATT&CK Mapping and CISA’s Decider Tool.