In recent months, a series of attacks targeting users of Barracuda Email Security Gateway (ESG) appliances has come to light. Security researchers have continually been uncovering new layers of sophistication in these attacks, and their latest discovery is a third novel backdoor, dubbed ‘Whirlpool’ malware. The US Cybersecurity and Infrastructure Security Agency (CISA) has issued a detailed advisory regarding this malicious software, highlighting its capabilities and potential risks. This article provides an in-depth analysis of the Whirlpool malware and how it fits into the larger picture of the Barracuda ESG attacks.
Discovery of third novel backdoor
The cybersecurity community has been working diligently to unravel the inner workings of the attacks on Barracuda ESG users. During their investigation, security researchers stumbled upon a previously unknown backdoor, now known as the “Whirlpool” malware. This discovery adds another layer of complexity to the already sophisticated attack campaign.
CISA’s advisory on the malware
To aid organizations in their defense against such threats, the US Cybersecurity and Infrastructure Security Agency has released a comprehensive advisory on the Whirlpool malware. The advisory provides technical details on the functionality of the malware, shedding light on the methods employed by the attackers.
Using arguments to establish a TLS reverse shell
One of the key features of the Whirlpool malware is its utilization of arguments to establish a Transport Layer Security (TLS) reverse shell. By taking two arguments, namely a C2 (Command and Control) IP and a port number, the malware creates a secure channel for communication between the attacker and the compromised device. This approach allows the attackers to maintain remote access and control over the targeted systems.
Addition of ‘Submarine’ Backdoor
This latest discovery comes on the heels of another backdoor known as ‘Submarine,’ which was revealed in a previous CISA update. The existence of multiple backdoors highlights the complexity and sophistication of the attack campaign targeting Barracuda ESG users. It is believed that the Whirlpool and Submarine malware may have been developed by the same threat actor or used in coordination to exploit vulnerabilities.
Barracuda Networks’ response
Barracuda Networks, the provider of the ESG appliances, has responded proactively to the attack campaign. In June, the company made the unusual decision to offer all users of their Email Security Gateway appliance a replacement device. This approach was taken to ensure that customers could protect themselves against the ongoing attacks and potential future threats.
Exploitation of zero-day vulnerability
The Barracuda ESG attacks were made possible by the exploitation of a zero-day vulnerability, tracked as CVE-2023-2868. This vulnerability allowed the threat actor to gain unauthorized access to the appliances and execute malicious actions. The attacks, which had been ongoing since October 2022, were brought to the attention of Barracuda on May 19. The company promptly patched the zero-day vulnerability two days later.
Identification of threat actor
Following a thorough investigation, the cybersecurity firm Mandiant revealed that the likely perpetrator behind the Barracuda ESG attacks is a Chinese Advanced Persistent Threat (APT) group known as UNC4841. This attribution sheds light on the motives and potential political or economic objectives of the attackers.
Barracuda’s response and patching of zero-day vulnerabilities
Barracuda Networks took swift action upon discovering the attacks and promptly patched the zero-day vulnerability. The company’s response demonstrated its commitment to the security and protection of its customers. By addressing the vulnerability and urging customers to replace their appliances, Barracuda took proactive steps to mitigate the risks posed by the attack campaign.
Utilization of other malware variants
In addition to the Whirlpool and Submarine backdoors, the threat actor behind the Barracuda ESG attacks also deployed other malware variants. Among these were the Seaside malware, which had been previously identified, and two previously unknown variants named Saltwater and Seaspy. The utilization of multiple malware variants highlights the sophisticated nature of the attack campaign, aimed at exploiting as many vulnerabilities as possible.
Urging customers to replace their appliances
Recognizing the persistent and evolving nature of the attacks, Barracuda Networks has made the decision to urge all customers to replace their Email Security Gateway appliances. This measure is recommended to ensure that customers have the latest secure devices to protect against present and future threats.
The discovery of the Whirlpool malware as the third novel backdoor in the Barracuda ESG attacks showcases the complexity and sophistication of the threat actor behind the campaign. The involvement of multiple backdoors, the exploitation of a zero-day vulnerability, and the utilization of various malware variants highlight the group’s relentless pursuit of compromising Barracuda ESG appliances. Organizations must remain vigilant, update their security measures, and follow the recommendations provided by Barracuda Networks and security authorities to protect themselves against this and similar threats in the future.