Critical Barracuda 0-Day Was Used To Backdoor Networks For 8 Months

A stylized skull and crossbones made out of ones and zeroes.

A critical vulnerability patched 10 days ago in widely used email software from IT security company Barracuda Networks has been under active exploitation since October. The vulnerability has been used to install multiple pieces of malware inside large organization networks and steal data, Barracuda said Tuesday.

The software bug, tracked as CVE-2023-2868, is a remote-command injection vulnerability that stems from incomplete input validation of user-supplied .tar files, which are used to pack or archive multiple files. When file names are formatted in a particular way, an attacker can execute system commands through the QX operator, a function in the Perl programming language that handles quotation marks. The vulnerability is present in the Barracuda Email Security Gateway versions through; Barracuda issued a patch 10 days ago.

On Tuesday, Barracuda notified customers that CVE-2023-2868 has been under active exploitation since October in attacks that allowed threat actors to install multiple pieces of malware for use in exfiltrating sensitive data out of infected networks.

“Users whose appliances we believe were impacted have been notified via the ESG user interface of actions to take,” Tuesday’s notice stated. “Barracuda has also reached out to these specific customers. Additional customers may be identified in the course of the investigation.”

Malware identified to date includes packages tracked as Saltwater, Seaside, and Seaspy. Saltwater is a malicious module for the SMTP daemon (bsmtpd) that the Barracuda ESG uses. The module contains backdoor functionality that includes the ability to upload or download arbitrary files, execute commands, and provide proxy and tunneling capabilities.

Seaside is an x64 executable in ELF (executable and linkable format), which stores binaries, libraries, and core dumps on disks in Linux and Unix-based systems. It provides a persistence backdoor that poses as a legitimate Barracuda Networks service and establishes itself as a PCAP filter for capturing data packets flowing through a network and performing various operations. Seaside monitors tracking on port 25, which is used for SMTP-based email.

It can be activated using a “magic packet” that’s known only to the attacker but appears innocuous to all others. Mandiant, the security firm Barracuda hired to investigate the attacks, said it found code in Seaspy that overlaps with the publicly available cd00r backdoor.

Seaside, meanwhile, is a module for the Barracuda SMTP daemon (bsmtpd) that monitors commands, including SMTP HELO/EHLO to receive a command-and-control IP address and port to establish a reverse shell.

Tuesday’s notice includes cryptographic hashes, IP addresses, file locations, and other indicators of compromise associated with the exploit of CVE-2023-2868 and the installation of the malware. Company officials also urged all impacted customers to take the following actions:

  1. Ensure your ESG appliance is receiving and applying updates, definitions, and security patches from Barracuda. Contact Barracuda support ( to validate if the appliance is up to date.
  2. Discontinue the use of the compromised ESG appliance and contact Barracuda support ( to obtain a new ESG virtual or hardware appliance.
  3. Rotate any applicable credentials connected to the ESG appliance:
    o  Any connected LDAP/AD
    o  Barracuda Cloud Control
    o  FTP Server
    o  SMB
    o  Any private TLS certificates
  4. Review your network logs for any of the [indicators of compromise] and any unknown IPs. Contact if any are identified.

The Cybersecurity and Infrastructure Security Agency added CVE-2023-2868 to its list of known exploited vulnerabilities on Friday.