Zyxel Firewall Flaw Let Attackers Execute Remote Code

Four new vulnerabilities have been discovered in some of the Zyxel Firewall and access point (AP) versions that are associated with Denial of Service, OS Command Injection, and Remote code execution.

These vulnerabilities have been assigned with CVE-2023-6397, CVE-2023-6398, CVE-2023-6399, and CVE-2023-6764.

The severity of these vulnerabilities ranges between 6.5 (Medium) and 8.1 (High). However, Zyxel networks have fixed these vulnerabilities, and a security advisory has been released to address these vulnerabilities.

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Zyxel Firewall Flaw

CVE-2023-6397: Null Pointer Dereference vulnerability in Zyxel

This vulnerability could allow a LAN-based threat actor to cause a denial-of-service condition by downloading a crafted RAR compressed file onto a LAN-side host if the firewall has “Anti-Malware” feature enabled.

The severity for this vulnerability has been given as 6.5 (Medium).

CVE-2023-6398: Post-authentication Command Injection vulnerability

This vulnerability exists in the file upload binary in Zyxel ATP series devices that could allow an authentication threat actor to execute operating system commands on the affected device via FTP with administrative privileges.

The severity for this vulnerability has been given as 7.2 (High).

CVE-2023-6399: Format String Vulnerability in Zyxel

This vulnerability allows an authenticated IPSec VPN user to perform a denial of service condition against the deviceid daemon.

Successful exploitation of this vulnerability involves sending a crafted hostname to an affected device if the device has the “Device Insight” feature enabled.

The severity for this vulnerability has been given as 5.7 (Medium).

CVE-2023-6764: Format String Vulnerability in Zyxel leading to Unauthenticated RCE

This vulnerability exists in one of the functions of the IPSec VPN feature that could allow a threat actor to achieve unauthenticated remote code execution on the affected device by sending a sequence of specially crafted payloads with an invalid pointer. 

However, this attack requires a detailed knowledge of the affected device’s memory layout and configuration. The severity for this vulnerability has been given as 8.1 (High).

Affected Products And Versions

Users of these products are recommended to upgrade to the latest versions in order to prevent these vulnerabilities from getting exploited by threat actors.

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