Zone transfer (AXFR)
A zone transfer (AXFR), defined in RFC 5936, is the DNS mechanism a secondary nameserver uses to copy an entire zone's records in one bulk request from the primary authoritative server, rather than querying one record at a time the way ordinary resolution works. It exists for legitimate nameserver replication, but an authoritative server misconfigured to answer AXFR requests from any client, not just its designated secondaries, hands an attacker the domain's complete record set in a single query -- every subdomain, mail server, and internal-sounding hostname at once, information otherwise only discoverable by guessing. Modern DNS providers restrict AXFR to an explicit allow-list of secondary IPs by default; a domain owner can confirm their own setup doesn't permit open transfers rather than assuming it's locked down.
By AdminKit team, Netbase JSC · Updated