Pierluigi Paganini September 16, 2021

The FBI, CISA, and the Coast Guard Cyber Command (CGCYBER) warn of state-sponsored attacks that are actively exploiting CVE-2021-40539 Zoho flaw.

The FBI, CISA, and the Coast Guard Cyber Command (CGCYBER) warn that nation-state APT groups are actively exploiting a critical vulnerability, tracked as CVE-2021-40539, in the Zoho ManageEngine ADSelfService Plus software.

ManageEngine ADSelfService Plus is self-service password management and single sign-on solution.

“This joint advisory is the result of analytic efforts between the Federal Bureau of Investigation (FBI), United States Coast Guard Cyber Command (CGCYBER), and the Cybersecurity and Infrastructure Security Agency (CISA) to highlight the cyber threat associated with active exploitation of a newly identified vulnerability (CVE-2021-40539) in ManageEngine ADSelfService Plus—a self-service password management and single sign-on solution.” reads the joint advisory. “The exploitation of ManageEngine ADSelfService Plus poses a serious risk to critical infrastructure companies, U.S.-cleared defense contractors, academic institutions, and other entities that use the software.”

According to the US agencies, threat actors can trigger the flaw to place webshells, which enable the adversary to conduct post-exploitation activities, such as compromising administrator credentials, conducting lateral movement, and exfiltrating registry hives and Active Directory files.

In early September, Zoho released a security patch to address an authentication bypass vulnerability, tracked as CVE-2021-40539, in its ManageEngine ADSelfService Plus. The company also warns the vulnerability is already exploited in attacks in the wild.

The vulnerability resides in the REST API URLs in ADSelfService Plus and could lead to remote code execution (RCE).

“We have addressed an authentication bypass vulnerability affecting the REST API URLs in ADSelfService Plus. This article provides more information on the issue and how to resolve it.” reads the advisory published by the company. “This vulnerability allows an attacker to gain unauthorized access to the product through REST API endpoints by sending a specially crafted request. This would allow the attacker to carry out subsequent attacks resulting in RCE.”

“This is a critical issue. We are noticing indications of this vulnerability being exploited,” Zoho added.

The flaw affects ADSelfService Plus 6113 release and prior, the flaw was addressed with the release of build 6114 or later.

The exploitation of the CVE-2021-40539 flaw poses a serious risk to organizations such as critical infrastructure companies and U.S.-cleared defense contractors.

Once compromised ManageEngine ADSelfService Plus, the attackers uploaded a zip archive containing a JavaServer Pages (JSP) webshell masquerading as an x509 certificate.

“Subsequent requests are then made to different API endpoints to further exploit the victim’s system.” continues the alert. “After the initial exploitation, the JSP webshell is accessible at /help/admin-guide/Reports/ReportGenerate.jsp. The attacker then attempts to move laterally using Windows Management Instrumentation (WMI), gain access to a domain controller, dump NTDS.dit and SECURITY/SYSTEM registry hives, and then, from there, continues the compromised access.”

FBI, CISA, and CGCYBER urge organizations to immediately update their installs.

“Additionally, FBI, CISA, and CGCYBER strongly recommend domain-wide password resets and double Kerberos Ticket Granting Ticket (TGT) password resets if any indication is found that the NTDS.dit file was compromised.” concludes the alert. Impacted organizations should Immediately report as an incident to CISA or the FBI  the existence of any of the following:

• Identification of indicators of compromise as outlined above.
• Presence of webshell code on compromised ManageEngine ADSelfService Plus servers.
• Unauthorized access to or use of accounts.
• Evidence of lateral movement by malicious actors with access to compromised systems.
• Other indicators of unauthorized access or compromise.”

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Pierluigi Paganini

(SecurityAffairs – hacking, Zoho)

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