Firefox has DNS leak security issue

[LeslieAlexander]

When I was using a proxy to surf the Internet, to ensure my security, I checked the DNS leak status. When I use Firefox, the query results show that my DNS is leaked and the DNS is my real DNS. However, when I use Chrome to query, there is no DNS leak. This is a serious security issue. Please Mozilla in time. repair. (The website I used to query DNS leaks is https://ipleak.net)

[JonesBones]

Might be caused by WebRTC. Try to set media.peerconnection.enabled to False under about:config if test in that site does not say "No leak" for WebRTC test.

Also might be caused by DNS over HTTPS.

[Anonymous]

No, the issue still there. I'm in China. My proxy is in Switzerland. It detected my DNS from China and Switzerland.

[Chloé]

I’ve encountered the same issue. In Firefox version 122, there is a DNS leak even though I haven’t installed any extensions. I’ve disabled WebRTC and DNS over HTTPS features, but the problem persists. When I switch to Edge with the same proxy configuration, there is no DNS leak.

[Chloé]

If you are using the Clash Meta new kernel, please consider switching back to version 1.16.0. This should prevent DNS leaks. 

[LeslieAlexander]

No, I use V2RayN

[Bunnyben]

Browsers must maintain users' privacy and security, especially when using proxies or VPNs. Here are a few steps you can take to mitigate this issue:

1. Update Firefox: Ensure you're using the latest version of Firefox. Developers often release updates to address security vulnerabilities and improve overall performance.

2. Check Firefox Settings: Review Firefox's settings related to DNS and proxy configurations. Sometimes, misconfigurations or conflicting settings can lead to leaks.

3. Use Firefox DNS-over-HTTPS (DoH): Firefox supports DNS-over-HTTPS, which encrypts DNS queries and helps prevent DNS leaks. You can enable this feature in Firefox's settings.

4. Report the Issue to Mozilla: If you've confirmed the DNS leak issue persists in the latest version of Firefox and after checking your settings, consider reporting it to Mozilla. They take security and privacy seriously and will investigate and address the issue if necessary.

5. Consider Alternative Browsers: While waiting for a fix, you may want to use an alternative browser like Chrome or another trusted option that doesn't exhibit the same DNS leak problem.

6. Use a DNS Leak Testing Tool: Continuously monitor your browser's behavior using DNS leak testing tools like the one you mentioned (ipleak.net) to ensure your privacy and security are maintained.

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[LeslieAlexander]

Whether I turn on DNS Over Https or not, The issue is still there. So How Can I report it to Mozilla? The reason I post here is precisely because I want Mozzilla to fix this problem.

[LeslieAlexander]

I found that in the latest Firefox Version 123.0 this issue is still there. Please fix it as quickly as possible

[Gorman42]

I find the same problem. Tried everything but FF still leaks DNS. Same configuration in Chromium does not.

[jscher2000]

If I understand how this test works, the result means that Firefox is not sending DNS requests through the proxy server, it is still using the same DNS servers as when you are not using a proxy.

Could you check the Connection Settings dialog? There is a checkbox at the bottom related to sending DNS requests through the proxy. I have not tested it myself. Here is the support article:

https://support.mozilla.org/kb/connection-settings-firefox

Meanwhile, if you use about:config, you also can confirm that the network.proxy.socks_remote_dns preference is set to true after saving that change.

Any difference on the DNS leak test?

[Yuqian]

Tried enable network.proxy.socks_remote_dns, leaks still persist. Under the same env, Edge does not leak. FYI, using the latest 124.0.2.

Update: Force using DoH resolve the issue, but Edge does require this.

[lilly]

In the meantime, you can try a few workarounds to mitigate the issue:

1. Enable DNS over HTTPS (DoH) in Firefox. This can help encrypt your DNS queries and prevent leaks. To do this, go to Settings > General > Network Settings > Settings, and select "Enable DNS over HTTPS".
2. Use a VPN (Virtual Private Network) extension in Firefox. This can help encrypt your internet traffic and prevent DNS leaks.
3. Consider using a different browser, like Chrome, which appears to be working correctly for you.

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