SAC125 - SSAC Report on Registrar Nameserver Management
Abstract
During domain registration, a minimum of two nameservers are typically required, and this
remains a requirement for any future updates to the domain. Often, domains are delegated to
nameservers that are subordinate to some other domains, creating inter-domain dependencies.
This network of dependencies creates a scenario where the functionality of a domain depends
on the operational status of another domain. This setup lacks contractual or procedural
safeguards against disruption or misuse, especially when the nameserver parent domain expires.
Most registries forbid deleting an expired domain if other domains depend on it for name
resolution. These constraints aim to prevent disruptions in DNS resolution for the dependent
domains. However, this also means that the expired domain remains in a liminal state, neither
fully operational nor completely removed. When registrars cannot delete expired domains with
dependents, they are forced to bear the burden of sponsoring the domain without remuneration
from the registrant. A peer-reviewed study, "Risky BIZness: Risks derived from Registrar Name
Management," observed that some registrars have found and utilized a loophole to these
constraints by renaming the host objects that are subordinate to the expiring domain.1 Once
renamed, the host objects are what Akiwate et al.—and subsequently the SSAC—refers to as
sacrificial nameservers.
This report focuses on a specific type of sacrificial nameserver where the parent domains of the renamed host objects are considered to be unsafe because they are registrable. Registrable
parent domains of sacrificial nameservers introduce a new attack surface for domain resolution
hijacking, as malicious actors can exploit unsafe sacrificial nameservers to gain unauthorized
control over the dependent domains, leading to manipulation or disruption. Unlike traditional
domain hijacking techniques that exploit compromised account credentials or manipulate the
resolution protocol, this report focuses on this unforeseen risk arising from a longstanding
practice employed by some registrars.
In this report, the SSAC explores potential solutions to remediate exposed domains and prevent
the creation of new unsafe sacrificial nameservers. The SSAC examines each proposed solution for its feasibility, effectiveness, and potential to reduce the attack surface without introducing undue complexity or new vulnerabilities into the DNS ecosystem.
remains a requirement for any future updates to the domain. Often, domains are delegated to
nameservers that are subordinate to some other domains, creating inter-domain dependencies.
This network of dependencies creates a scenario where the functionality of a domain depends
on the operational status of another domain. This setup lacks contractual or procedural
safeguards against disruption or misuse, especially when the nameserver parent domain expires.
Most registries forbid deleting an expired domain if other domains depend on it for name
resolution. These constraints aim to prevent disruptions in DNS resolution for the dependent
domains. However, this also means that the expired domain remains in a liminal state, neither
fully operational nor completely removed. When registrars cannot delete expired domains with
dependents, they are forced to bear the burden of sponsoring the domain without remuneration
from the registrant. A peer-reviewed study, "Risky BIZness: Risks derived from Registrar Name
Management," observed that some registrars have found and utilized a loophole to these
constraints by renaming the host objects that are subordinate to the expiring domain.1 Once
renamed, the host objects are what Akiwate et al.—and subsequently the SSAC—refers to as
sacrificial nameservers.
This report focuses on a specific type of sacrificial nameserver where the parent domains of the renamed host objects are considered to be unsafe because they are registrable. Registrable
parent domains of sacrificial nameservers introduce a new attack surface for domain resolution
hijacking, as malicious actors can exploit unsafe sacrificial nameservers to gain unauthorized
control over the dependent domains, leading to manipulation or disruption. Unlike traditional
domain hijacking techniques that exploit compromised account credentials or manipulate the
resolution protocol, this report focuses on this unforeseen risk arising from a longstanding
practice employed by some registrars.
In this report, the SSAC explores potential solutions to remediate exposed domains and prevent
the creation of new unsafe sacrificial nameservers. The SSAC examines each proposed solution for its feasibility, effectiveness, and potential to reduce the attack surface without introducing undue complexity or new vulnerabilities into the DNS ecosystem.
