A patch for the vulnerability, which has been exploited since October 2022, had been issued by Barracuda last month to stop the exploit from allowing ESG backdooring.
“The vulnerability existed in a module which initially screens the attachments of incoming emails,” the company had said previously. “No other Barracuda products, including our SaaS email security services, were subject to the vulnerability identified.”
Users whose appliances Barracuda believed were impacted are being notified via the ESG user interface of actions to take. Barracuda has also reached out to these specific customers.
Replacement advised despite patches
The vulnerability, dubbed CVE-2023-2868, was identified on May 19, 2023, and reportedly affected versions 5.1.3.001 through 9.2.0.006, allowing a remote attacker to achieve code execution on susceptible installations.
Consequently, Barracuda released patches on May 20 and May 21 for all ESG appliances worldwide. In the latest update on the incident, however, the company has advised to replace the appliance irrespective of their patch status.
“Impacted ESG appliances must be immediately replaced regardless of patch version level,” the company said in an update, adding that its “remediation recommendation at this time is a full replacement of the impacted ESG.”
Multi-strained malware used
Three different malware strains have been discovered to date on a subset of appliances allowing for persistent backdoor access, according to the company. Evidence of data exfiltration was identified on a subset of impacted appliances, the company said in a previous update.
The different strains used — SALTWATER, SEASPY, and SEASIDE — were all backdoor modules affecting data exfiltration. While both SALTWATER and SEASIDE help establish a hack for the Barracuda SMTP daemon (bsmtpd) equipped to upload and download arbitrary files, execute commands, and tunnel malicious traffic, SEASPY is an x64 executable and linkable format (ELF) backdoor offering persistence capabilities, activated through a magic (remote, wake-on-LAN) packet.
Mandiant, the Google-owned cybersecurity intelligence firm investigating the incident, has revealed source code overlaps between SEASPY and an open source backdoor called cd00r. Attacks have not been attributed to any known threat actor or group.