Taiwan-based networking device manufacturer Zyxel is urging customers to update the firmware of ATP, USG Flex, VPN, and ZyWALL/USG firewall devices, to prevent the exploitation of recently patched vulnerabilities.
Tracked as CVE-2023-28771, CVE-2023-33009 and CVE-2023-33010, the issues can lead to OS command execution, remote code execution (RCE), and denial-of-service (DoS).
The first of the issues came to light in late April, when Zyxel released patches for it, warning that it can be exploited remotely without authentication by sending specially crafted packets to a vulnerable device.
In mid-May, after security researchers reproduced the exploit targeting CVE-2023-28771, Rapid7 warned that the vulnerability would likely be mass-exploited in the wild, considering that there were tens of thousands of Zyxel device web interfaces accessible from the internet.
Shortly after, a Mirai variant was seen exploiting the bug to ensnare unpatched devices in a DDoS-capable botnet. Around the same time, Zyxel released patches for CVE-2023-33009 and CVE-2023-33010.
Now, Zyxel once again raises the alarm on the ongoing attacks, urging customers to install the available patches as soon as possible, to prevent exploitation.
The manufacturer notes that it previously alerted customers of the available patches through multiple channels, including security advisory newsletter, push notifications via web GUIs, and scheduled firmware upgrades for cloud-based devices.
The company also advises customers to disable HTTP/HTTPS services from the WAN if unused, enable policy control and only allow access from trusted IPs, enable geoIP filtering, and disable UDP ports 500 and 4500 if unused.
To identify potential malware infections, customers should look for symptoms such as unresponsive devices, unreachable web GUIs or SSH management interfaces, network interruptions, and disconnecting VPN connections.
Additional information on the addressed vulnerabilities can be found on Zyxel’s security advisories page.