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.
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.