uBlock Blocking Requests with Proxy: How to Fix It

uBlock blocks all requests to domains when using a proxy server due to a conflict between the extension’s DNS API and proxy settings. This occurs due to the “CNAME uncloaking” feature (cnameUncloak) which was added in uBlock Origin 1.25 and is only available in Firefox. To resolve the issue, you need to disable this feature or properly configure the interaction between uBlock and proxy extensions.

Contents

• Problem Cause
• Configuring uBlock to Work with Proxy
• Alternative Solutions
• Step-by-Step Instructions
• Testing and Verification

Problem Cause

The main reason for blocking all domains when using a proxy server is related to the specific operation of the DNS API in uBlock Origin. As explained in research, starting from version 1.25, uBlock Origin uses a Firefox-specific DNS API to block “cloaked” first-party trackers.

Important: This feature allows uBlock to detect and block requests to third-party domains that are disguised as subdomains of the main site through CNAME records. However, when using a proxy server, a conflict occurs in DNS request processing.

The problem manifests in that when a proxy is enabled (especially through an extension like FoxyProxy), uBlock continues to send DNS requests through system settings rather than through the proxy, which leads to:

• Discovery of real IP addresses instead of proxy addresses
• Traffic routing conflicts
• Blocking of legitimate requests

Configuring uBlock to Work with Proxy

To solve the problem, there are several approaches to configuring uBlock Origin:

1. Disabling the CNAME Uncloaking Feature

The most effective way is to disable the cnameUncloak function in uBlock settings:

1. Open uBlock Origin settings
2. Go to the “Advanced” or “Advanced user mode” tab
3. Find the cnameUncloak parameter and set it to false

As noted in one source, this setting specifically helps avoid DNS leaks when using a proxy.

2. Configuring DNS over HTTPS

In Firefox settings, you can change DNS over HTTPS parameters:

• Go to about:preferences#privacy
• In the “Network Protection” section, change DNS over HTTPS settings to “Off” or “High Protection”
• In “Connection Settings” change “Use system proxy settings” to “No proxy”

3. Synchronizing Proxy Settings

Ensure that proxy settings are consistent between Firefox and extensions:

• In FoxyProxy, check that “Send DNS through SOCKS5 proxy” is enabled
• In uBlock, ensure there are no conflicting filtering rules

Alternative Solutions

If basic settings don’t help, let’s consider additional options:

Using Alternative Blocking Methods

1. Disabling Dynamic Filtering

   • Enable “advanced user mode” in uBlock
   • Disable dynamic filtering for proxy connections

2. Manual Filter Configuration

   • Create a whitelist for important domains
   • Use “My Rules” instead of “My Filters” for blocking rules

Extension Replacement

In extreme cases, consider:

• Using other ad blockers that work better with proxies
• Combining uBlock with other tools for proxy management

Step-by-Step Instructions

Here’s a detailed instruction for solving the problem:

1. Disable uBlock Origin during configuration
2. Open uBlock settings (extension icon > Settings)
3. Go to Advanced user mode (if not enabled)
4. Find the cnameUncloak parameter in settings and set it to false
5. Restart the browser
6. Check proxy operation with uBlock disabled
7. Enable uBlock and verify correct operation

If the problem persists:

1. Open about:config in Firefox
2. Find the parameter network.proxy.socks_remote_dns
3. Set the value to true
4. Restart Firefox

Testing and Verification

After configuration, you need to check:

DNS Leak Testing

• Use services like dnsleaktest.com
• Compare results with uBlock enabled and disabled
• Ensure that IP address is not exposed when using a proxy

Functional Testing

• Load sites through proxy with uBlock enabled
• Check loading of subdomains and external resources
• Ensure that ads are blocked while legitimate content loads

Traffic Monitoring

• Use developer tools in Firefox
• Check network requests in the “Network” tab
• Ensure that legitimate requests are not being blocked

Sources

1. GitHub Issue - uBlock Origin v1.25.0 new feature cause DNS leaks
2. VPN Reviewer - uBlock Origin Firefox add-on causing DNS leaks
3. Bleeping Computer - uBlock Origin 1.25 blocks cloaked first-party scripts
4. Mozilla Support - Firefox and uBlock Origin
5. GitHub - uBlock supports DNS leak with DOH and proxy
6. FoxyProxy issue with uBlock and SOCKS5

Conclusion

The problem of uBlock blocking all domains when using a proxy server is a known issue related to the interaction between the extension’s DNS API and Firefox proxy settings. The main solutions include:

1. Disabling the cnameUncloak feature in uBlock settings - this is the most effective method
2. Proper configuration of DNS over HTTPS and proxy in Firefox
3. Synchronization of settings between uBlock and proxy extensions

If basic settings don’t help, you can consider using alternative blocking methods or temporarily disabling some uBlock features. It’s important to regularly check settings and test functionality after making changes to ensure both security and functionality simultaneously.

For additional information, always refer to the official uBlock Origin documentation and the project’s GitHub repository, where similar issues are discussed and solutions are provided.