# APT Actors Chaining Vulnerabilities Against SLTT, Critical Infrastructure, and Elections Organizations

**us-cert.cisa.gov/ncas/alerts/aa20-283a**

## Summary

_This joint cybersecurity advisory uses the MITRE Adversarial Tactics, Techniques, and_
_Common Knowledge (ATT&CK®) framework. See the_ _[ATT&CK for Enterprise framework for](https://attack.mitre.org/versions/v7/matrices/enterprise/)_
_all referenced threat actor techniques._

**Note: the analysis in this joint cybersecurity advisory is ongoing, and the information**
provided should not be considered comprehensive. The Cybersecurity and
Infrastructure Security Agency (CISA) will update this advisory as new information is
available.

This joint cybersecurity advisory was written by CISA with contributions from the Federal
Bureau of Investigation (FBI).

CISA has recently observed advanced persistent threat (APT) actors exploiting multiple
legacy vulnerabilities in combination with a newer privilege escalation vulnerability—CVE2020-1472—in Windows Netlogon. The commonly used tactic, known as vulnerability
chaining, exploits multiple vulnerabilities in the course of a single intrusion to compromise a
network or application.

This recent malicious activity has often, but not exclusively, been directed at federal and
state, local, tribal, and territorial (SLTT) government networks. Although it does not appear
these targets are being selected because of their proximity to elections information, there
may be some risk to elections information housed on government networks.

CISA is aware of some instances where this activity resulted in unauthorized access to
elections support systems; however, CISA has no evidence to date that integrity of elections
data has been compromised. There are steps that election officials, their supporting SLTT IT
staff, and vendors can take to help defend against this malicious cyber activity.

Some common tactics, techniques, and procedures (TTPs) used by APT actors include
leveraging legacy network access and virtual private network (VPN) vulnerabilities in
[association with the recent critical CVE-2020-1472 Netlogon vulnerability. CISA is aware of](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
multiple cases where the Fortinet FortiOS Secure Socket Layer (SSL) VPN vulnerability
[CVE-2018-13379 has been exploited to gain access to networks. To a lesser extent, CISA](https://nvd.nist.gov/vuln/detail/CVE-2018-13379)
[has also observed threat actors exploiting the MobileIron vulnerability CVE-2020-15505.](https://nvd.nist.gov/vuln/detail/CVE-2020-15505)
While these exploits have been observed recently, this activity is ongoing and still unfolding.


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[After gaining initial access, the actors exploit CVE-2020-1472 to compromise all Active](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
Directory (AD) identity services. Actors have then been observed using legitimate remote
access tools, such as VPN and Remote Desktop Protocol (RDP), to access the environment
with the compromised credentials. Observed activity targets multiple sectors and is not
limited to SLTT entities.

CISA recommends network staff and administrators review internet-facing infrastructure for
these and similar vulnerabilities that have or could be exploited to a similar effect, including
[Juniper CVE-2020-1631, Pulse Secure CVE-2019-11510, Citrix NetScaler CVE-2019-19781,](https://nvd.nist.gov/vuln/detail/CVE-2020-1631)
[and Palo Alto Networks CVE-2020-2021 (this list is not considered exhaustive).](https://nvd.nist.gov/vuln/detail/CVE-2020-2021)

[Click here for a PDF version of this report.](https://us-cert.cisa.gov/sites/default/files/publications/AA20-283A-APT_Actors_Chaining_Vulnerabilities.pdf)

## Technical Details

 Initial Access

APT threat actors are actively leveraging legacy vulnerabilities in internet-facing
infrastructure (Exploit Public-Facing Application [[T1190], External Remote Services](https://attack.mitre.org/versions/v7/techniques/T1190/) [[T1133])](https://attack.mitre.org/versions/v7/techniques/T1133/)
to gain initial access into systems. The APT actors appear to have predominately gained
[initial access via the Fortinet FortiOS VPN vulnerability CVE-2018-13379.](https://nvd.nist.gov/vuln/detail/CVE-2018-13379)

Although not observed in this campaign, other vulnerabilities, listed below, could be used to
gain network access (as analysis is evolving, these listed vulnerabilities should not be
considered comprehensive). As a best practice, it is critical to patch all known vulnerabilities
within internet-facing infrastructure.

[Citrix NetScaler CVE-2019-19781](https://nvd.nist.gov/vuln/detail/CVE-2019-19781)
[MobileIron CVE-2020-15505](https://nvd.nist.gov/vuln/detail/CVE-2020-15505)
[Pulse Secure CVE-2019-11510](https://nvd.nist.gov/vuln/detail/CVE-2019-11510)
[Palo Alto Networks CVE-2020-2021](https://nvd.nist.gov/vuln/detail/CVE-2020-2021)
F5 BIG-IP [CVE-2020-5902](https://nvd.nist.gov/vuln/detail/CVE-2020-5902)

**Fortinet FortiOS SSL VPN CVE-2018-13379**

[CVE-2018-13379 is a path traversal vulnerability in the FortiOS SSL VPN web portal. An](https://nvd.nist.gov/vuln/detail/CVE-2018-13379)
unauthenticated attacker could exploit this vulnerability to download FortiOS system files
[through specially crafted HTTP resource requests.[1]](https://www.fortiguard.com/psirt/FG-IR-18-384)

## MobileIron Core & Connector Vulnerability CVE-2020-15505

[CVE-2020-15505 is a remote code execution vulnerability in MobileIron Core & Connector](https://nvd.nist.gov/vuln/detail/CVE-2020-15505)
[versions 10.3 and earlier.[2] This vulnerability allows an external attacker, with no privileges,](https://www.mobileiron.com/en/blog/mobileiron-security-updates-available)
to execute code of their choice on the vulnerable system. As mobile device management


-----

(MDM) systems are critical to configuration management for external devices, they are
usually highly permissioned and make a valuable target for threat actors.

## Privilege Escalation

Post initial access, the APT actors use multiple techniques to expand access to the
[environment. The actors are leveraging CVE-2020-1472 in Windows Netlogon to escalate](https://nvd.nist.gov/vuln/detail/CVE-2020-1472)
privileges and obtain access to Windows AD servers. Actors are also leveraging the
opensource tools such as Mimikatz and the CrackMapExec tool to obtain valid account
credentials from AD servers (Valid Accounts [[T1078]).](https://attack.mitre.org/versions/v7/techniques/T1078/)

**Microsoft Netlogon Remote Protocol Vulnerability: CVE-2020-1472**

[CVE-2020-1472 is a vulnerability in Microsoft Windows Netlogon Remote Protocol (MS-](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
[NRPC), a core authentication component of Active Directory.[3] This vulnerability could allow](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
an unauthenticated attacker with network access to a domain controller to completely
compromise all AD identity services (Valid Accounts: Domain Accounts [[T1078.002]).](https://attack.mitre.org/versions/v7/techniques/T1078/002/)
Malicious actors can leverage this vulnerability to compromise other devices on the network
(Lateral Movement [[TA0008]).](https://attack.mitre.org/versions/v7/tactics/TA0008/)

## Persistence

Once system access has been achieved, the APT actors use abuse of legitimate credentials
[(Valid Accounts [T1078]) to log in via VPN or remote access services (External Remote](https://attack.mitre.org/versions/v7/techniques/T1078/)
_Services_ [[T1133]) to maintain persistence.](https://attack.mitre.org/versions/v7/techniques/T1133/)

## Mitigations

Organizations with externally facing infrastructure devices that have the vulnerabilities listed
in this joint cybersecurity advisory, or other vulnerabilities, should move forward with an
“assume breach” mentality. As initial exploitation and escalation may be the only observable
exploitation activity, most mitigations will need to focus on more traditional network hygiene
and user management activities.

## Keep Systems Up to Date

Patch systems and equipment promptly and diligently. Establishing and consistently
maintaining a thorough patching cycle continues to be the best defense against adversary
TTPs. See table 1 for patch information on CVEs mentioned in this report.

_Table 1: Patch information for CVEs_

**Vulnerability** **Vulnerable Products** **Patch Information**


-----

**Vulnerability** **Vulnerable Products** **Patch Information**


CVE-201813379

CVE-201919781

CVE-20205902

CVE-201911510

CVE-202015505


FortiOS 6.0: 6.0.0 to 6.0.4
FortiOS 5.6: 5.6.3 to 5.6.7
FortiOS 5.4: 5.4.6 to 5.4.12

Citrix Application Delivery Controller
Citrix Gateway
Citrix SDWAN WANOP

Big-IP devices (LTM, AAM, Advanced
WAF, AFM, Analytics, APM, ASM,
DDHD, DNS, FPS, GTM, Link
Controller, PEM, SSLO, CGNAT)

Pulse Connect Secure 9.0R1 9.0R3.3, 8.3R1 - 8.3R7, 8.2R1 8.2R12, 8.1R1 - 8.1R15
Pulse Policy Secure 9.0R1 - 9.0R3.1,
5.4R1 - 5.4R7, 5.3R1 - 5.3R12, 5.2R1

- 5.2R12, 5.1R1 - 5.1R15

MobileIron Core & Connector
versions 10.3.0.3 and earlier,
10.4.0.0, 10.4.0.1, 10.4.0.2, 10.4.0.3,
10.5.1.0, 10.5.2.0 and 10.6.0.0
Sentry versions 9.7.2 and earlier, and
9.8.0;
Monitor and Reporting Database
(RDB) version 2.0.0.1 and earlier


Fortinet Security
[Advisory: FG-IR-18-](https://www.fortiguard.com/psirt/FG-IR-18-384)
384

Citrix blog post:
firmware updates for
[Citrix ADC and Citrix](https://www.citrix.com/blogs/2020/01/19/vulnerability-update-first-permanent-fixes-available-timeline-accelerated/)
Gateway versions 11.1
and 12.0
Citrix blog post:
security updates for
[Citrix SD-WAN](https://www.citrix.com/blogs/2020/01/22/update-on-cve-2019-19781-fixes-now-available-for-citrix-sd-wan-wanop/)
WANOP release
10.2.6 and 11.0.3
Citrix blog post:
firmware updates for
[Citrix ADC and Citrix](https://www.citrix.com/blogs/2020/01/23/fixes-now-available-for-citrix-adc-citrix-gateway-versions-12-1-and-13-0/)
Gateway versions 12.1
and 13.0
Citrix blog post:
firmware updates for
Citrix ADC and Citrix
Gateway version 10.5

F5 Security Advisory:
K52145254: TMUI
RCE vulnerability
CVE-2020-5902

Pulse Secure Out-ofCycle Advisory:
Multiple vulnerabilities
[resolved in Pulse](https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44101)
Connect Secure /
Pulse Policy Secure
9.0RX

MobileIron Blog:
[MobileIron Security](https://www.mobileiron.com/en/blog/mobileiron-security-updates-available)
Updates Available


-----

**Vulnerability** **Vulnerable Products** **Patch Information**


CVE-20201631

CVE-20202021

CVE-20201472


Junos OS 12.3, 12.3X48, 14.1X53,
15.1, 15.1X49, 15.1X53, 17.2, 17.3,
17.4, 18.1, 18.2, 18.3, 18.4, 19.1,
19.2, 19.3, 19.4, 20.1

PAN-OS 9.1 versions earlier than
PAN-OS 9.1.3; PAN-OS 9.0 versions
earlier than PAN-OS 9.0.9; PAN-OS
8.1 versions earlier than PAN-OS
8.1.15, and all versions of PAN-OS
8.0 (EOL)

Windows Server 2008 R2 for x64based Systems Service Pack 1
Windows Server 2008 R2 for x64based Systems Service Pack 1
(Server Core installation)
Windows Server 2012
Windows Server 2012 (Server Core
installation)
Windows Server 2012 R2
Windows Server 2016
Windows Server 2019
Windows Server 2019 (Server Core
installation)
Windows Server, version 1903
(Server Core installation)
Windows Server, version 1909
(Server Core installation)
Windows Server, version 2004
(Server Core installation)


Juniper Security
Advisory JSA11021

Palo Alto Networks
[Security Advisory for](https://security.paloaltonetworks.com/CVE-2020-2021)
CVE-2020-2021

Microsoft Security
[Advisory for CVE-](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
2020-1472


## Comprehensive Account Resets

If there is an observation of [CVE-2020-1472 Netlogon activity or other indications of valid](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
credential abuse detected, it should be assumed the APT actors have compromised AD
administrative accounts, the AD forest should not be fully trusted, and, therefore, a new
forest should be deployed. Existing hosts from the old compromised forest cannot be
migrated in without being rebuilt and rejoined to the new domain, but migration may be done
through “creative destruction,” wherein as endpoints in the legacy forest are
decommissioned, new ones can be built in the new forest. This will need to be completed on
on-premise as well as Azure-hosted AD instances.


-----

Note that fully resetting an AD forest is difficult and complex; it is best done with the
assistance of personnel who have successfully completed the task previously.

It is critical to perform a full password reset on all user and computer accounts in the AD
forest. Use the following steps as a guide.

1. Create a temporary administrator account, and use this account only for all

administrative actions
[2. Reset the Kerberos Ticket Granting Ticket ( krbtgt ) password [4]; this must be](https://docs.microsoft.com/en-us/windows-server/identity/ad-ds/manage/ad-forest-recovery-resetting-the-krbtgt-password)

completed before any additional actions (a second reset will take place in step 5)
3. Wait for the krbtgt reset to propagate to all domain controllers (time may vary)
4. Reset all account passwords (passwords should be 15 characters or more and

randomly assigned):

1. User accounts (forced reset with no legacy password reuse)
2. Local accounts on hosts (including local accounts not covered by Local

Administrator Password Solution [LAPS])
3. Service accounts
4. Directory Services Restore Mode (DSRM) account
5. Domain Controller machine account
6. Application passwords
5. Reset the `krbtgt password again`
6. Wait for the `krbtgt reset to propagate to all domain controllers (time may vary)`
7. Reboot domain controllers
8. Reboot all endpoints

The following accounts should be reset:

AD Kerberos Authentication Master (2x)
All Active Directory Accounts
All Active Directory Admin Accounts
All Active Directory Service Accounts
All Active Directory User Accounts
DSRM Account on Domain Controllers
Non-AD Privileged Application Accounts
Non-AD Unprivileged Application Accounts
Non-Windows Privileged Accounts
Non-Windows User Accounts
Windows Computer Accounts
Windows Local Admin

## CVE-2020-1472

To secure your organization’s Netlogon channel connections:


-----

**Update all Domain Controllers and Read Only Domain Controllers. On August 11,**
[2020, Microsoft released software updates to mitigate CVE-2020-1472. Applying this](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1472)
update to domain controllers is currently the only mitigation to this vulnerability (aside
from removing affected domain controllers from the network).
**Monitor for new events, and address non-compliant devices that are using**
vulnerable Netlogon secure channel connections.
**Block public access to potentially vulnerable ports, such as 445 (Server Message**
Block [SMB]) and 135 (Remote Procedure Call [RPC]).

[To protect your organization against this CVE, follow advice from Microsoft, including:](https://support.microsoft.com/en-us/help/4557222/how-to-manage-the-changes-in-netlogon-secure-channel-connections-assoc)

Update your domain controllers with an update released August 11, 2020, or later.
Find which devices are making vulnerable connections by monitoring event logs.
Address non-compliant devices making vulnerable connections.
[Enable enforcement mode to address CVE-2020-1472 in your environment.](https://nvd.nist.gov/vuln/detail/CVE-2020-1472)

## VPN Vulnerabilities

Implement the following recommendations to secure your organization’s VPNs:

**Update VPNs, network infrastructure devices, and devices being used to remote**
into work environments with the latest software patches and security configurations.
[See CISA Tips Understanding Patches and Software Updates and](https://us-cert.cisa.gov/ncas/tips/ST04-006) Securing Network
Infrastructure Devices. Wherever possible, enable automatic updates. See table 1 for
patch information on VPN-related CVEs mentioned in this report.
**Implement multi-factor authentication (MFA) on all VPN connections to increase**
**security. Physical security tokens are the most secure form of MFA, followed by**
authenticator app-based MFA. SMS and email-based MFA should only be used when
no other forms are available. If MFA is not implemented, require teleworkers to use
[strong passwords. See CISA Tips Choosing and Protecting Passwords and](https://us-cert.cisa.gov/ncas/tips/ST04-002)
[Supplementing Passwords for more information.](https://us-cert.cisa.gov/ncas/tips/ST05-012)

Discontinue unused VPN servers. Reduce your organization’s attack surface by
discontinuing unused VPN servers, which may act as a point of entry for attackers. To protect
your organization against VPN vulnerabilities:

**Audit configuration and patch management programs.**
**Monitor network traffic for unexpected and unapproved protocols, especially outbound**
to the internet (e.g., Secure Shell [SSH], SMB, RDP).
**Implement MFA, especially for privileged accounts.**
**Use separate administrative accounts on separate administration workstations.**
**Keep** [software up to date. Enable automatic updates, if available.](https://us-cert.cisa.gov/ncas/tips/ST04-006)

## How to uncover and mitigate malicious activity


-----

**Collect and remove for further analysis:**

Relevant artifacts, logs, and data.
**Implement mitigation steps that avoid tipping off the adversary that their presence in**
the network has been discovered.
**Consider soliciting incident response support from a third-party IT security**
organization to:

Provide subject matter expertise and technical support to the incident response.
Ensure that the actor is eradicated from the network.
Avoid residual issues that could result in follow-up compromises once the incident
is closed.

## Resources

[CISA VPN-Related Guidance](https://www.cisa.gov/vpn-related-guidance)
CISA Infographic: Risk Vulnerability And Assessment (RVA) Mapped to the MITRE
ATT&CK FRAMEWORK
[National Security Agency InfoSheet: Configuring IPsec Virtual Private Networks](https://media.defense.gov/2020/Jul/02/2002355501/-1/-1/0/CONFIGURING_IPSEC_VIRTUAL_PRIVATE_NETWORKS_2020_07_01_FINAL_RELEASE.PDF)
CISA Joint Advisory: AA20-245A: Technical Approaches to Uncovering and
Remediating Malicious Activity
CISA Activity Alert: [AA20-073A: Enterprise VPN Security](https://us-cert.cisa.gov/ncas/alerts/aa20-073a)
CISA Activity Alert: [AA20-031A: Detecting Citrix CVE-2019-19781](https://us-cert.cisa.gov/ncas/alerts/aa20-031a)
CISA Activity Alert: AA20-010A: Continued Exploitation of Pulse Secure VPN
Vulnerability
**[Cybersecurity Alerts and Advisories: Subscriptions to CISA Alerts and](https://public.govdelivery.com/accounts/USDHSUSCERT/subscriber/new)** MS-ISAC
Advisories

## Contact Information

Recipients of this report are encouraged to contribute any additional information that they
may have related to this threat.

For any questions related to this report or to report an intrusion and request resources for
incident response or technical assistance, please contact:

[CISA (888-282-0870 or Central@cisa.dhs.gov), or](http://10.10.0.46/mailto:Central@cisa.dhs.gov)
[The FBI through the FBI Cyber Division (855-292-3937 or CyWatch@fbi.gov) or a](http://10.10.0.46/mailto:CyWatch@fbi.gov) local
field office

**_DISCLAIMER_**

_This information is provided "as is" for informational purposes only. The United States_
_Government does not provide any warranties of any kind regarding this information. In no_
_event shall the United States Government or its contractors or subcontractors be liable for_
_any damages, including but not limited to, direct, indirect, special or consequential damages,_


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_arising out of, resulting from, or in any way connected with this information, whether or not_
_based upon warranty, contract, tort, or otherwise, whether or not arising out of negligence,_
_and whether or not injury was sustained from, or arose out of the results of, or reliance upon_
_the information._

_The United States Government does not endorse any commercial product or service,_
_including any subjects of analysis. Any reference to specific commercial products,_
_processes, or services by service mark, trademark, manufacturer, or otherwise, does not_
_constitute or imply their endorsement, recommendation, or favoring by the United States_
_Government._

## References

 Revisions

October 9, 2020: Initial Version

October 11, 2020: Updated Summary

October 12, 2020: Added Additional Links

[This product is provided subject to this Notification and this](https://us-cert.cisa.gov/privacy/notification) [Privacy & Use policy.](https://www.dhs.gov/privacy-policy)

**Please share your thoughts.**

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