Two zero-day vulnerabilities were being used by two different groups to infiltrate DrayTek Vigor enterprise routers and switch devices, enabling the attackers to access traffic and install backdoors.

The invasive action was noticed first on Dec. 4, 2019 by Netlab 360 researchers affecting the Vigor2960 v1.5.1, Vigor300B v1.5.1 and Vigor3900 v1.5.1 routers along with the VigorSwitch20P2121 v2.3.2, VigorSwitch20G1280 v2.3.2, VigorSwitch20P1280 v2.3.2, VigorSwitch20G2280 v2.3.2 and VigorSwitch20P2280 v2.3.2.

“With the help of 360 Firmware Total system, we are able to perform vulnerability research. The two 0-day vulnerability command injection points are keyPath and rtick, located in the /www/cgi-bin/mainfunction.cgi, and the corresponding Web Server program is /usr/sbin/lighttpd,” Netlab said.

The threat actors were exploiting an unauthorized remote command execution vulnerability and taking advantage of the fact that DrayTek uses two password transmission methods: plain text and an RSA encrypted transmission that is susceptible to manipulation. The former problem is self-explanatory, while the latter exists because keyPath does not have very strong input control, which makes unauthorized remote command execution possible, Netlab said.

The first threat group known to be going after these devices used the keyPath vulnerability to download malware capable of listening in on network traffic through ports 21, 25, 143 and 110. The malware ran in the background and sent data dumps to its command server every Monday, Wednesday and Friday.

The second gang used the rtick command injection vulnerability to spoof the captcha function, to gain access and then to create two sets of web session backdoors, an SSH backdoor and finally a system backdoor.

On Dec. 25, 2019, Netlab posted a note on Twitter and informed several national CERTs, describing the zero-day IoC without mentioning the vendor or products involved, as the manufacturer had not yet addressed the problems. DrayTek on Feb. 10, 2020 issued a security bulletin and patches to rectify the problem.

For admins who have not or cannot update their device firmware, DrayTek said, “If you have remote access enabled on your router, disable it if you don’t need it, and use an access control list if possible. If you have not updated the firmware yet, disable remote access (admin) and SSL VPN. The ACL does not apply to SSL VPN connections (Port 443) so you should also temporarily disable SSL VPN until you have updated the firmware.”