Hackers have gained access to government networks by combining VPN and Windows bugs, the Federal Bureau of Investigation (FBI) and the Cybersecurity and Infrastructure Security Agency (CISA) said in a joint security alert published on Friday.
Attacks have targeted federal and state, local, tribal, and territorial (SLTT) government networks. Attacks against non-government networks have also been detected, the two agencies said.
"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," the security alert reads.
"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," officials also added.
Attacks chained Fortinet VPN and Windows Zerologon bugs
CVE-2018-13379 is a vulnerability in the Fortinet FortiOS Secure Socket Layer (SSL) VPN, an on-premise VPN server designed to be used as a secure gateway to access enterprise networks from remote locations.
The CVE-2018-13379, disclosed last year, allows attackers to upload malicious files on unpatched systems and take over Fortinet VPN servers.
CVE-2020-1472, also known as Zerologon, is a vulnerability in Netlogon, the protocol used by Windows workstations to authenticate against a Windows Server running as a domain controller.
The vulnerability allows attackers to take over domain controllers, servers users to manage entire internal/enterprise networks and usually contain the passwords for all connected workstations.
CISA and the FBI say attackers are combining these two vulnerabilities to hijack Fortinet servers and then pivot and take over internal networks using Zerologon.
"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," the two agencies also added.
The joint alert didn't provide details about the attackers except to describe them as "advanced persistent threat (APT) actors."
Both CISA and the FBI recommended that entities in both the private and public US sector update systems to patch the two bugs, for which patches have been available for months.
In addition, CISA and the FBI also warned that hackers could swap the Fortinet bug for any other vulnerability in VPN and gateway products that have been disclosed over the past few months and which provide similar access.
Citrix "ADC" servers and Citrix network gateways (CVE-2019-19781)
MobileIron mobile device management servers (CVE-2020-15505)
F5 BIG-IP network balancers (CVE-2020-5902)
All the vulnerabilities listed above provide "initial access" to servers often used on the edge of enterprise and government networks. These vulnerabilities can also be easily chained with the Zerologon Windows bug for similar attacks as the Fortinet+Zerologon intrusions observed by CISA.