DNS Leak

DNS Leak Test (dnsleak.com) is a diagnostic tool that tests whether a VPN or proxy connection is properly routing DNS queries through the secure tunnel or is leaking DNS requests to the user's regular ISP DNS resolver. It reveals which DNS servers are processing name resolution queries from the current connection.

For OSINT investigators relying on VPNs for operational security, DNS leak testing is a critical pre-investigation verification step. A DNS leak occurs when the operating system or browser sends DNS queries outside the VPN tunnel — to the ISP's DNS servers rather than the VPN provider's servers. When this happens, the ISP can see which domains the investigator is looking up, even though web traffic routes through the VPN.

DNS leaks are common because of how VPN software interacts with operating system DNS resolution, particularly on Windows. The operating system may fall back to its configured DNS servers when the VPN's DNS server is slow or unavailable, creating intermittent leaks that are difficult to detect without testing.

DNS Leak Test sends multiple DNS queries through the browser and reports which DNS servers responded. If servers appear that belong to the investigator's ISP (rather than to the VPN provider or another privacy-respecting DNS service), a DNS leak is confirmed.

For TOR users, DNS leaks are particularly serious because the entire value of TOR anonymization depends on all traffic routing through the TOR network. A DNS leak bypasses TOR for name resolution, revealing research activity to the ISP.

Proper DNS leak remediation depends on the VPN client — some clients offer DNS leak protection settings that force all DNS queries through the VPN tunnel. Alternatively, configuring a trusted DNS provider (Cloudflare 1.1.1.1, NextDNS, or the VPN's DNS) at the operating system level can prevent leaks.

Document DNS leak test results as part of pre-investigation operational security verification, recording which DNS servers were detected and whether the VPN configuration passed the test.