Hackers Exploiting a Critical Vulnerability in Zyxel Firewall & VPN Devices

Several hackers have newly begun exploiting a recently patched critical vulnerability, identified as CVE-2022-30525, which is affecting business firewall and VPN devices from Zyxel.

In response to this vulnerability, the cybersecurity experts at Rapid7 have discovered that a number of Zyxel firewalls supporting ZTP like the ATP series, the VPN series, and the USG FLEX series, are vulnerable to this security flaw.

The exploit can enable an attacker to trigger an arbitrary command injection remotely without having to authenticate, enabling the setting up of a reverse shell in most cases.

Affected Models & Firmware Versions

Here below we have mentioned all the affected models along with their respective firmware versions:-

• USG FLEX 100, 100W, 200, 500, 700 (Firmware: ZLD5.00 thru ZLD5.21 Patch 1)
• USG20-VPN, USG20W-VPN (Firmware: ZLD5.10 thru ZLD5.21 Patch 1)
• ATP 100, 200, 500, 700, 800 (Firmware: ZLD5.10 thru ZLD5.21 Patch 1)

Both small branch deployments and corporate headquarters deployments of the affected firewall are advertised. 

VPN solutions, as well as SSL inspection, web filtering, intrusion protection, and email security, are provided by the company, which advertises a throughput of up to 5GB per second through its firewalls.

It has been noted that the European Union is the region with the most potential vulnerabilities, with France and Italy having the largest numbers.

Over 15,000 of these affected models are visible on the Shodan site, which indicates that they are relatively popular.

It is possible to remotely inject commands into the affected models via the administrative HTTP interface without authenticating via the HTTP API. Here, the “nobody” user is used to execute all commands on the server. 

Lib_wan_settings.py contains the vulnerability that an attacker can exploit by bypassing unsanitized attacker input into the os.system method, due to the fact that /ztp/cgi-bin/handler URI has been used to exploit this vulnerability.

This vulnerability is triggered by the setWanPortSt command which is invoked in conjunction with the vulnerable functionality.

Metasploit Module

It has been found that this vulnerability has been exploited by a Metasploit module. A nobody Meterpreter session can be established by using the Metasploit module.

On top of that, Metasploit engages in the injection of commands into the mtu field.

Recommendation

Zyxel’s uncoordinated disclosure was discovered by Rapid7 independently on May 9, 2015. And this issue was addressed by Zyxel on April 28, 2022, in a patch release.

It is highly recommended that you install the vendor patch as soon as possible. If you have an automatic firmware update option, make sure that it is enabled. Inspect the web interface that you use to manage the system and disable WAN access.

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