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 make use of 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 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 who received your Zyxel device from an ISP, we recommend you reach out to the ISP support team directly, as the device may have custom-built settings.

For end-users who purchased the Zyxel devices on your own, please contact your local Zyxel support team or visit our forum if you require further assistance.

Got a question or a tipoff?

Please contact your local service rep for further information or assistance. If you’ve found a vulnerability, we want to work with you to fix it—contact security@zyxel.com.tw and we’ll get right back to you.

Acknowledgment

Thanks to CERT/CC for reporting the issue to us.

Revision history

2021-1-21: Initial release
2021-2-1: Updated the WSQ50 firmware schedule and removed NBG418v2 as it’s not affected
2021-3-11: Updated the list of affected CPE and ONTs
2022-3-16: Updated the firmware schedule for NBG6515 and NBG6615