What Is a DNS Leak?

Abisola | Feb 11, 2026

A DNS leak happens when domain name lookups leave a VPN or proxy tunnel and reach the ISP or local resolver instead. Those queries can expose which hostnames you tried to reach, even when page content later loads over HTTPS. Privacy tools fail their job when DNS does not follow the same protected path as the rest of the traffic.

Without a VPN, the operating system sends DNS to configured resolvers, often the ISP. With a VPN, the client should steer all traffic, including DNS, through the tunnel to the provider’s resolver so the ISP only sees encrypted packets to the VPN endpoint. Related privacy controls include DNS over HTTPS.

Normal resolution versus a broken path

Leaks appear when another interface wins the race, when IPv6 queries bypass an IPv4-only tunnel, when a transparent DNS proxy on the ISP network captures wayward lookups, or when split tunneling leaves DNS on the local stack. WebRTC and some browser features can also reveal addresses in ways users do not expect; those are related privacy issues, not always classified as DNS leaks, but they show up in the same audits.

Testing involves visiting a reputable leak test page or inspecting which resolver answers your queries while the VPN claims to be connected. Corporate networks sometimes force internal DNS for compliance. Consumer VPNs should document how they pin DNS while connected.

Why marketers and fraud teams care

DNS leakage is primarily a user privacy topic, but it intersects proxy and VPN policy. Businesses ask whether paid traffic comes from privacy tools; our VPN blocking FAQ explains product stance. Aggressive blocking of all privacy tech creates false positives, while ignoring anonymization entirely invites suspicious behavior from scripted clicks.

Operational teams also harden employee laptops so research traffic does not accidentally expose strategy through leaked queries on café Wi-Fi. That is closer to security than click fraud, yet the same network hygiene reduces espionage-style scraping that can inform ad fraud schemes. Soft context: site bot detection and campaign quality are separate from fixing a leaky VPN client.

Frequently Asked Questions

  • How do I know if I have a DNS leak?

    Connect your VPN, then run a DNS leak test from a trusted site and check which resolvers answer. If you see your ISP resolver instead of the VPN provider’s DNS, you have a leak. Also compare IPv4 and IPv6 results, because one stack can leak while the other stays inside the tunnel.

  • How do you fix a DNS leak?

    Use a VPN client that forces all DNS through the tunnel, disable conflicting adapters, and turn off IPv6 if the tunnel does not cover it. Prefer providers that support DNS leak protection and DNS over HTTPS where available. Retest after each change. Corporate users should follow IT policy for internal resolvers.

  • What happens when DNS leaks?

    Your DNS queries may reach the ISP or another local resolver in a form that reveals which hostnames you looked up. Page content can still be encrypted with HTTPS, but the names you resolve are exposed. For privacy tools that promise to hide browsing from the ISP, a leak breaks that promise for those lookups.

Abisola

Abisola

Abisola handles content and support at ClickPatrol. She helps customers get more value from cleaner traffic data and writes practical resources about ad fraud, fake traffic, and smarter PPC decisions.