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CISA Releases Malware Analysis Reports on Barracuda Backdoors

CISA has published three malware analysis reports on malware variants associated with exploitation of CVE-2023-2868. CVE-2023-2868 is a remote command injection vulnerability affecting Barracuda Email Security Gateway (ESG) Appliance, versions 5.1.3.001-9.2.0.006. It was exploited as a zero day as early as October 2022 to gain access to ESG appliances. According to industry reporting, the actors exploited the vulnerability to gain initial access to victim systems and then implanted backdoors to establish and maintain persistence.

CISA analyzed backdoor malware variants obtained from an organization that had been compromised by threat actors exploiting the vulnerability.

  • Barracuda Exploit Payload and Backdoor – The payload exploits CVE-2023-2868, leading to dropping and execution of a reverse shell backdoor on ESG appliance. The reverse shell establishes communication with the threat actor’s command and control (C2) server, from where it downloads the SEASPY backdoor to the ESG appliance. The actors delivered the payload to the victim via a phishing email with a malicious attachment.
  • SEASPY – SEASPY is a persistent and passive backdoor that masquerades as a legitimate Barracuda service. SEASPY monitors traffic from the actor’s C2 server. When the right packet sequence is captured, it establishes a Transmission Control Protocol (TCP) reverse shell to the C2 server. The shell allows the threat actors to execute arbitrary commands on the ESG appliance.
  • SUBMARINE – SUBMARINE is a novel persistent backdoor executed with root privileges that lives in a Structured Query Language (SQL) database on the ESG appliance. SUBMARINE comprises multiple artifacts—including a SQL trigger, shell scripts, and a loaded library for a Linux daemon—that together enable execution with root privileges, persistence, command and control, and cleanup. CISA also analyzed artifacts related to SUBMARINE that contained the contents of the compromised SQL database. This malware poses a severe threat for lateral movement.

For more information, including indicators of compromise and YARA rules for detection, on the exploit payload, SEASPY, and SUBMARINE backdoor, see the following Malware Analysis Reports:

For more information on CVE-2023-2868 see, Barracuda’s page Barracuda Email Security Gateway Appliance (ESG) Vulnerability and Mandiant’s blogpost Barracuda ESG Zero-Day Vulnerability (CVE-2023-2868) Exploited Globally by Aggressive and Skilled Actor.

To report suspicious or criminal activity related to information found in these malware analysis reports, contact CISA’s 24/7 Operations Center at Report@cisa.gov or (888) 282-0870.