Multiple Barracuda Networks products feature an undocumented backdoor, leaving widely deployed data centre kit vulnerable to hijacking.

Secret privileged user accounts were found in various Barracuda appliances, including its flagship Spam and Virus Firewall, Web Application Firewall, Web Filter, SSL VPN, and other gear. The accounts cannot be disabled, are hard-wired into the equipment's operating system, and can be accessed remotely via SSH or the local terminal.

Once logged into a vulnerable machine, hackers can run programs and take over the networking device. The accounts, which were found in /etc/passwd and /etc/shadow files in the equipment, use weak passwords that are easy to crack, security researchers claimed.

Each appliance uses a firewall to block access to the SSH server, and thus the hidden root accounts, unless the connection originates from an IP address in the private network ranges of 192.168.200.0/24 and 192.168.10.0/24. The firewall rules also allow in network traffic from public IP addresses in the 205.158.110.0/24 and 216.129.105.0/24 ranges - some of which are controlled by Barracuda, but the others are not.

Therefore a successful compromise would need to be launched from one of these IP addresses at a reachable, vulnerable Barracuda device. Network administrators may want to firewall off port 22 completely.

The oversight is tricky to exploit and was discovered by SEC Consult of Austria, which published an advisory on the issue today.

"An attacker is able to access all mentioned Barracuda appliances through weak passwords and gain shell access to execute arbitrary code on the appliances, e.g. in order to install further backdoors, change configuration or take over the system," explained Johannes Greil of SEC Consult.

"Those attacks are possible from within the two large IP address ranges from the Internet, and two private IP address ranges. One hacked system or malicious company in those networks will allow an attacker to take over all externally reachable Barracuda appliances worldwide."

Barracuda acknowledged the cock-up but downplayed the risk. It also released a software update called "Security Definition 2.0.5", which tightened up its account security but does not remove the hidden root, remote and cluster users because they are needed to administer remote support for customers.

In a related advisory, SEC Consult said Barracuda VPN kit allowed an "unauthenticated attacker to download configuration files and database dumps".

Steve Pao, VP for Product Management at Barracuda Networks, told El Reg that the undocumented superuser accounts were established for support purposes but admitted the setup was flawed and promised to pay SEC Consulting an unspecified bounty for finding the vulnerability.

"The specific discovery was related to access from the default limited set of IP addresses used by the system to initiate remote support tunnels to Barracuda Technical Support," Pao told El Reg in a statement. "We have released a security definition to existing Barracuda Networks appliances that minimises potential attack vectors.

"Individual customers should contact Barracuda Networks Technical Support if they need more information. As we do with all issues reported through our 'Bug Bounty' programme, we have acknowledged the SEC Consulting's reporting of the issues in both the release notes with our security definition and on the Tech Alerts section of our Web site."

Stefan Viehböck of SEC Consult led the research into the vulnerabilities. Barracuda has published alerts covering both bugs on its website here. ®