Zyxel security advisory for DNSpooq

CVE: CVE-2020-25681, CVE-2020-25682, CVE-2020-25683, CVE-2020-25684, CVE-2020-25685, CVE-2020-25686, CVE-2020-25687

Summary

Zyxel will release patches for products affected by the Dnsmasq vulnerabilities reported by CERT/CC. Users are advised to install the applicable firmware updates or follow the best practices for optimal protection.

What is the vulnerability?

Dnsmasq, open-source software that provides DNS forwarding and caching, has two sets of vulnerabilities, as listed below. Dubbed as DNSpooq, these vulnerabilities could allow an attacker to corrupt memory on the target device and perform cache poisoning attacks against the target environment.

• Memory corruption vulnerabilities due to boundary checking errors in DNSSEC handling code. (CVE-2020-25681, CVE-2020-25682, CVE-2020-25683, and CVE-2020-25687)
• DNS response validation vulnerabilities that can result in DNS cache poisoning. (CVE-2020-25684, CVE-2020-25685, and CVE-2020-25686)

What versions are vulnerable—and what should you do?

After a thorough investigation, we’ve identified products that use the Dnsmasq software and confirmed that these products are only affected by the DNS response validation vulnerabilities with medium severity. We’ll include the solution in the affected products’ next regular firmware releases to address the issues, as shown in the table below. For optimal protection, we urge users to install the applicable updates when they become available or follow CERT/CC’s best practices when protecting DNS infrastructure before the firmware updates become available:

• Protect your DNS clients and DNS client software using a stateful-inspection firewall that can provide application security.
• Provide secure DNS recursion service with features such as DNSSEC validation and the interim 0x20-bit encoding as part of enterprise DNS services where applicable.
• Prevent exposure of IoT devices and lightweight devices directly over the Internet to minimize abuse of DNS.
• Regularly update software and embedded firmware to the latest available version and the recommended secure configuration suitable for your operations environment (e.g., disable caching if not needed or provided by an upstream server).

Please note that the table does NOT include customized models for internet service providers (ISPs). For ISP customers, please contact your Zyxel representative for further details. For end-users, please contact your local Zyxel support team or visit our forum if you require further assistance.