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NXNSAttack: New DNS Vulnerability Allows Big DDoS Attacks

Several major providers of DNS services and software have been working to address a serious DNS vulnerability that could allow malicious actors to launch significant distributed denial-of-service (DDoS) attacks.

Several major providers of DNS services and software have been working to address a serious DNS vulnerability that could allow malicious actors to launch significant distributed denial-of-service (DDoS) attacks.

The vulnerability, dubbed NXNSAttack, was discovered by a team of researchers from Tel Aviv University and Interdisciplinary Center Herzliya in Israel.

The flaw exists in the DNS protocol and it affects all recursive DNS resolvers. It has been confirmed to impact DNS software such as NLnet Labs’s Unbound, BIND, Knot Resolver and PowerDNS, as well as DNS services provided by Google, Microsoft, Cloudflare, Amazon, Oracle (DYN), Verisign, IBM Quad9, and ICANN.

The affected organizations have patched their software and servers to prevent exploitation. However, entities that operate their own DNS resolver need to update their software as soon as possible to prevent attacks.

Various CVE identifiers have been assigned by the impacted vendors, including CVE-2020-8616 (BIND), CVE-2020-12662 (Unbound), CVE-2020-12667 (Knot) and CVE-2020-10995 (PowerDNS).

DNS amplification attacks are DDoS attacks where the attacker exploits vulnerabilities in DNS servers to turn small queries into larger payloads that can disrupt the targeted server.

In the case of NXNSAttack, a remote attacker can amplify network traffic by sending DNS queries to a vulnerable resolver, which queries an authoritative server controller by the attacker. The attacker’s server delegates to fake server names pointing to the victim’s DNS domain, causing the resolver to generate queries towards the victim’s DNS server. The attack can result in an amplification factor of over 1,620.

NXNSAttack - image credits NIC.CZ

The researchers who discovered the flaw have created a dedicated website for NXNSAttack and published a detailed paper describing their findings. CZ.NIC, which develops Knot Resolver, has also published a blog post that provides a summary of how the attack works.

Related: Hoaxcalls Botnet Expands Targets List, DDoS Capabilities

Related: Georgia Man Admits to Launching DDoS Attack

Related: HHS Says DDoS Attack Failed to Cause Disruption

Related: CISA Reminds Federal Agencies to Use Its DNS Service

Written By

Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.

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