CVE-2023-2868 – Barracuda Zero-Day Vulnerability

THE THREAT

On May 23rd, the email security company Barracuda disclosed a new vulnerability impacting Barracuda Email Security Gateway (ESG) appliances. Exploitation of the vulnerability, by threat actors in the wild, has been confirmed, and additional technical details relating to real-world attacks were shared by Barracuda in an update on May 30th.

The vulnerability tracked as CVE-2023-2868 (CVSS: 9.4) is a remote command injection vulnerability that impacts Barracuda ESG versions 5.1.3.001-9.2.0.006. A remote and unauthenticated threat actor may exploit the vulnerability to execute code on vulnerable assets, leading to deployment of malware and data theft. Exploitation of CVE-2023-2868 has been ongoing since at least October 2022.

Organizations are strongly recommended to validate patch deployment and review all potentially impacted devices for signs of compromise.

What we’re doing about it

• The eSentire Threat Intelligence team has performed threat hunts across the eSentire client base for known Indicators of Compromise
• IP addresses associated with real-world exploit are blocked via the eSentire Global Deny List
• eSentire Managed Vulnerability Service (MVS) will add plugins for this vulnerability as they become available
• The eSentire Threat Intelligence team will continue to track this topic for additional details and detection opportunities

What you should do about it

• Ensure all potentially impacted Barracuda Email Security Gateway Appliances are fully up-to-date on security patches
  • If required, contact Barracuda support ([email protected]) to verify application version

If exploitation has been confirmed /the organization has been contacted by Barracuda related to exploitation of CVE-2023-2868:

• Immediately discontinue use of the ESG appliance
• Notify the eSentire Security Operations Center to allow for additional investigation
• Reset all credentials connected to the ESG application
• Review logs for known Indicators of Compromise outlined in the Barracuda advisory

Additional information

Exploitation of CVE-2023-2868 is possible due to improper input validation of user-supplied .tar files. A remote attacker may format file names in a specific way to enable the remote execution of system commands via Perl's qx operator. Commands are executed under the same privileges as the ESG Gateway product, and no user interaction is required.

The investigation into CVE-2023-2868 and its exploitation remains ongoing at the time of writing. Barracuda has not confirmed how many organizations were impacted by attacks, but they do state that, “CVE-2023-2868 was utilized to obtain unauthorized access to a subset of ESG appliances” and “evidence of data exfiltration was identified on a subset of impacted appliances”. Barracuda has notified all organizations that were identified as being impacted by attacks exploiting CVE-2023-2868.

In real-world attacks, unidentified threat actors exploited the vulnerability for initial access into victim organizations. Once access was achieved, both novel and known customized malware were deployed to victim organizations. Observed malware includes:

• SALTWATER, a trojanized module for the Barracuda SMTP daemon (bsmtpd) that functions as a backdoor into victim organizations; the malware is capable of file upload/download, command execution, and proxy/tunneling
• SEASPY, a second backdoor malware that impersonates Barracuda Network service and “establishes itself as a PCAP filter, specifically monitoring traffic on port 25”
• SEASIDE, a Lua-based module used to establish a reverse shell on compromised assets

While no attribution has been given at this time, based on the exploitation of a zero-day vulnerability, the use of previously unseen malware, and the avoidance of any detection for seven months, it is probable that this campaign was carried out by a sophisticated and capable threat actor group that is well resourced.

References:

[1] https://status.barracuda.com/incidents/34kx82j5n4q9
[2] https://www.barracuda.com/company/legal/esg-vulnerability
[3] https://nvd.nist.gov/vuln/detail/CVE-2023-2868