CVE-2021-40539 ZOHO Bug Exploited By Nation State Actors

Cybersecurity experts has warned of an ongoing cyberespionage campaign that has already compromised at least nine organizations worldwide from critical sectors, including defense, healthcare, and energy.

Threat actors exploited a critical vulnerability, tracked as CVE-2021-40539, in the Zoho ManageEngine ADSelfService Plus software, which is self-service password management and single sign-on solution. The vulnerability resides in the REST API URLs in ADSelfService Plus and could lead to remote code execution (RCE).

As early as Sept. 17 the actor leveraged leased infrastructure in the United States to scan hundreds of vulnerable organizations across the internet. Subsequently, exploitation attempts began on Sept. 22 and likely continued into early October. During that window, the actor successfully compromised at least nine global entities across the technology, defense, healthcare, energy and education industries.”

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The analysis of the global telemetry revealed that attackers targeted at least 370 Zoho ManageEngine servers in the United States alone.

Following initial exploitation, a payload was uploaded to the victim network which installed a Godzilla webshell. Upon compromising the target systems by exploiting the CVE-2021-40539 flaw, the threat actors deployed Godzilla web shells on compromised servers to gain persistence to the victims’ networks.

Once webshell deployed, threat actors used additional tools deployed in a subset of compromised networks. The cyberactor also deployed a custom variant of an open-source backdoor written in Go language called NGLite and a credential-harvesting tool tracked as KdcSponge.

The NGLite backdoor allows running commands received through its C2 channel. Experts pointed out that the NGLite backdoor uses a novel C2 channel that leverages a decentralized network based on the legitimate NKN.

Experts also detailed the KdcSponge credential stealer, which hooks into the Windows LSASS API from within the LSASS process to steal credentials from inbound attempts to authenticate via the Kerberos service (“KDC Service”). KdcSponge allows capturing the domain name, username, and password. Once inside the target network, threat actors aim at exfiltrating sensitive information from local domain controllers, such as the Active Directory database file (ntds.dit) and the SYSTEM hive from the registry.

While experts have yet to attribute the campaign to a specific threat actor, they observed some similarities between the TTPs associated with Threat Group 3390 (TG-3390, Emissary Panda, APT27, Bronze Union, and Lucky Mouse). The APT group has been active since 2010, targeted organizations worldwide, including U.S. defense contractors, financial services firms, and a national data center in Central Asia.