The vulnerability stemmed from incomplete input validation of user-supplied .tar files. Credit: Seagate Barracuda has patched a zero-day vulnerability that had been exploited since October to backdoor customers’ Email Security Gateway (ESG) appliances with custom malware and steal data, the company said on Tuesday. “On May 19, 2023, Barracuda Networks identified a remote command injection vulnerability (CVE-2023-2868) present in the Barracuda Email Security Gateway (appliance form factor only) versions 5.1.3.001-9.2.0.006,” the company said, adding that the vulnerability stemmed from incomplete input validation of user-supplied .tar files as it pertains to the names of the files contained within the archive. Discovery and patching of the vulnerabilityBarracuda identified the vulnerability on May 19, a day after it was alerted about anomalous traffic originating from its ESG appliances. The vulnerability existed in a module that initially screens the attachments of incoming emails.On the following day, a security patch to remediate the vulnerability was applied to all ESG appliances worldwide. “On May 21, 2023, a script was deployed to all impacted appliances to contain the incident and counter unauthorized access methods. A series of security patches are being deployed to all appliances in furtherance of our containment strategy,” the company said. The earliest identified evidence of exploitation of the vulnerability was in October 2022. The vulnerability was utilized to obtain unauthorized access to a subset of ESG appliances. A malware was identified on a subset of appliances, allowing for persistent backdoor access. “Evidence of data exfiltration was identified on a subset of impacted appliances,” Barracuda said.The malware usedThere were several malware programs that were used to exploit the vulnerability. Barracuda has deployed Mandiant to investigate the same as well as links of the malware to any previously known backdoor.Saltwater is a trojanized module for the Barracuda SMTP daemon (bsmtpd) that contains backdoor functionality. The capabilities of Saltwater include the ability to upload or download arbitrary files, and execute commands, as well as proxy and tunneling capabilities, the company said.“The backdoor is implemented using hooks on the send, recv, close syscalls and amounts to five components, most of which are referred to as “Channels” within the binary,” the company said. The five channels are DownloadChannel, UploadChannel, ProxyChannel, ShellChannel, and TunnelArgs. Another malware strain deployed for the campaign is SeaSpy, designed to provide persistence and be activated using magic packets. “It helps monitor port 25 (SMTP) traffic, and some of its code overlaps with the publicly available cd00r passive backdoor,” Barracuda said.The threat actors also used a Lua-based module, called Seaside for the Barracuda SMTP daemon, that monitors SMTP HELO/EHLO commands to receive a command-and-control IP address and port which it passes as arguments to an external binary that establishes a reverse shell, the company said. Informing and safeguarding customersUsers whose appliances the company believes were impacted have been notified via the ESG user interface of actions to take. Barracuda has also reached out to these specific customers.The company has advised users to investigate their environments, probably to ensure the attackers move laterally to other devices on their network. It also advises customers to ensure their ESG appliance is receiving and applying updates, definitions, and security patches from Barracuda. Related content feature Top cybersecurity M&A deals for 2023 Fears of recession, rising interest rates, mass tech layoffs, and conservative spending trends are likely to make dealmakers cautious, but an ever-increasing need to defend against bigger and faster attacks will likely keep M&A activity steady in By CSO Staff Sep 22, 2023 24 mins Mergers and Acquisitions Mergers and Acquisitions Mergers and Acquisitions brandpost Unmasking ransomware threat clusters: Why it matters to defenders Similar patterns of behavior among ransomware treat groups can help security teams better understand and prepare for attacks By Joan Goodchild Sep 21, 2023 3 mins Cybercrime news analysis China’s offensive cyber operations support “soft power” agenda in Africa Researchers track Chinese cyber espionage intrusions targeting African industrial sectors. By Michael Hill Sep 21, 2023 5 mins Advanced Persistent Threats Cyberattacks Critical Infrastructure brandpost Proactive OT security requires visibility + prevention You cannot protect your operation by simply watching and waiting. It is essential to have a defense-in-depth approach. By Austen Byers Sep 21, 2023 4 mins Security Podcasts Videos Resources Events SUBSCRIBE TO OUR NEWSLETTER From our editors straight to your inbox Get started by entering your email address below. Please enter a valid email address Subscribe