Researchers have uncovered a worm that’s designed to plant backdoors on QNAP network-attached storage (NAS) devices. The malware is distributed through the exploitation of the GNU Bash vulnerability known as ShellShock.
Cybercriminals started exploiting ShellShock to gain full access to the contents of NAS devices developed by Taiwan-based QNAP shortly after the existence of the vulnerability came to light. The vendor released updates to address the flaw in its product at the beginning of October, but because the patches are not easy to apply many systems remain vulnerable.
The SANS Institute reports that a worm is currently spreading among QNAP devices, which run an embedded Linux operating system, by exploiting the Bash vulnerability.
“The attack targets a QNAP CGI script, ‘/cgi-bin/authLogin.cgi’, a well known vector for Shellshock on QNAP devices,” Johannes Ullrich of the SANS Internet Storm Center wrote in a blog post. “This script is called during login, and reachable without authentication. The exploit is then used to launch a simple shell script that will download and execute a number of additional pieces of malware.”
One of the worm’s malicious components is designed for click fraud and it targets the online advertisement network JuiceADV.
The threat also sets up backdoors on infected devices by creating an SSH server on port 26, by adding a user (named “request“) with administrator privileges, and by copying some CGI scripts with backdoor functionality to the “cgi-bin” directory. The malware modifies the “autorun.sh” file in order to run the backdoors on reboot.
Researchers have also noticed that the worm sets the DNS server on the infected machine to 184.108.40.206, which is actually Google’s DNS server. It’s possible that the attackers do this in order to get a more reliable DNS server, since as Ullrich explains, QNAP devices sometime use internal DNS servers which aren’t fully recursive. By using this method, the attackers might also be trying to evade potential logging mechanisms.
The worm is dangerous because it abuses infected systems to look for other vulnerable devices on the network, Ullrich noted.
Interestingly, the malware also patches the ShellShock vulnerability on infected devices by downloading the applying the security updates from QNAP. Experts believe the threat does this to prevent additional exploitation.
NAS devices are also a tempting target for ransomware attacks. This summer, a piece of ransomware dubbed SynoLocker was used to infect Synology NAS servers by exploiting a vulnerability that was patched in December 2013.