Russian nation-state hackers last spring capitalized on a misconfigured Cisco Duo multifactor authentication (MFA) account at a nongovernment organization and created their own device, with MFA, to infiltrate the victim's network, the FBI and Cybersecurity and Infrastructure Security Agency (CISA) warned this week in a joint advisory.
The attackers initially brute-forced their way to a set of user credentials that had been removed from the organization's MFA. They created a rogue account and then used it to exploit a known Windows Print Spooler vulnerability, aka PrintNightmare (CVE-2021-34527), to run their code using privileged user access and were able to access cloud and email accounts as a way to steal documents.
"Russian state-sponsored cyber actors gained initial access [TA0001] to the victim organization via compromised credentials [T1078] and enrolling a new device in the organization’s Duo MFA. The actors gained the credentials [TA0006] via brute-force password guessing attack [T1110.001], allowing them access to a victim account with a simple, predictable password. The victim account had been un-enrolled from Duo due to a long period of inactivity but was not disabled in the Active Directory. As Duo’s default configuration settings allow for the re-enrollment of a new device for dormant accounts, the actors were able to enroll a new device for this account, complete the authentication requirements, and obtain access to the victim network," the advisory says.
The FBI and CISA recommend reviewing MFA policies to prevent such a re-enrollment action, confirming that inactive accounts are disabled in Active Directory and MFA systems, and making sure all software is updated, patched, and not prone to known flaws.