DNS & Email Trust
high Severity
Free Check

Open DNS Resolver Vulnerability

Verifies authoritative nameservers do not permit recursive lookups for external IPs, preventing DNS amplification DDoS attacks.

Test Your Website for Open DNS Resolver Vulnerability

Run this check along with 90+ automated tests across your domain.

Why It Matters

Open recursive resolvers are weaponized by botnets to launch massive DNS reflection DDoS attacks against external victims.

How We Check This

We send recursive DNS query probes to domain nameservers for external domains (e.g. google.com) and verify they are rejected.

How to Fix & Implement

Copy-paste configuration blocks tailored for your web server or edge proxy.

nginx snippet
# In BIND named.conf: recursion no; additional-from-cache no;

Frequently Asked Questions

What is a DNS amplification attack?

Attackers spoof a victim’s IP and send small queries that generate 50x larger responses sent back to the victim.