Nation-state actors target critical sectors by exploiting the CVE-2021-40539 flaw

by chebbi abir

Experts warn of an ongoing hacking campaign that already compromised at least nine organizations worldwide from critical sectors by exploiting CVE-2021-40539.

Cybersecurity experts from Palo Alto Networks warn 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).

In the middle of September, the FBI, CISA, and the Coast Guard Cyber Command (CGCYBER) warned that nation-state APT groups were actively exploiting the CVE-2021-40539 flaw.

Experts also observed a series of unrelated attacks that failed to compromise their targets, these attacks have been attributed to separated threat actors.

“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.” reads the analysis published by Palo Alto Networks.

“Following initial exploitation, a payload was uploaded to the victim network which installed a Godzilla webshell.”

Palo Alto Networks researchers started observing scans for vulnerable servers on September 17, a few days after the joint alert published by CISA, the FBI, and the CGCYBER, and the first exploitation attempts began on September 22 and likely continued into early October.

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

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.

Following the deployment of the webshell, threat actors used additional tools deployed in a subset of compromised networks. The cyberspies 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.

“The NKN touts that their decentralized network uses a public blockchain and can support communication between millions of peers, each of which are identified by a unique NKN address instead of the typical network identifiers, such as IP addresses. Therefore, the immediate IP address that the NGLite tool communicates with in its C2 channel is just a peer in the decentralized network and is unlikely to represent the threat actor’s network location.” continues the analysis. “This design makes detection and prevention of the NGLite C2 communication channel difficult.”

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-3390Emissary PandaAPT27Bronze 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.

The group was involved in cyber espionage campaigns aimed at new generation weapons and in surveillance activities on dissidents and other civilian groups. 

The cyber espionage group leverage both readily available tools and custom malware in their operations, many tools are available for years, but in recent attacks, their code was updated.

The recent string of attacks launched by the cyber-espionage group took place in 2020 and aimed at several gambling companies.

The post published by Palo Alto Networks, includes Indicators of Compromise (IoCs) for the recent string of attacks.

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