Userscript Proxy

Browser extensions on iOS, Android and pretty much any other web browsing device. No jailbreak/root required.

Userscript Proxy is built around mitmproxy and acts as a MITM, injecting userscripts into web pages as they flow through it. Both HTTP and HTTPS are supported.

• Userscript Proxy
• Getting started
  • Security notice
  • Starting the proxy
  • On a mobile device
  • HTTPS
    • Android
    • iOS
  • Deploying userscripts
• Apps with certificate pinning
  • Basic pattern
    • Examples
  • Regular expression
    • Examples
• Data usage
• Userscript compatibility
• Options
  • --bypass-csp ALLOW
  • --inline, -i
  • --list-injected, -l
  • --no-default-rules
  • --no-default-userscripts
  • --port PORT, -p PORT
  • --query-param-to-disable PARAM, -q PARAM
  • --rules FILE
  • --transparent, -t
  • --userscripts-dir DIR, -u DIR
• Contribute

Getting started

Security notice

Make sure you understand these security aspects before using Userscript Proxy:

• You should run the proxy on your own server, because it can read and modify all traffic sent through it.
• You should not expose the proxy to incoming connections from the Internet, because then anyone can connect to it and use your Internet connection for whatever they want. In practice, this means that you should not add a port-forward for Userscript Proxy in your router. (Browsing the web via the proxy uses only outgoing connections, which is fine.)

Starting the proxy

1. Make sure you have Docker installed. This should work:

   docker --version
   

2. Start Userscript Proxy:

   docker run -t --rm --name userscript-proxy -p 8080:8080 alling/userscript-proxy
   

   When you see Proxy server listening at http://*:8080, the proxy is up and running.

3. Check that the proxy is working. There are two ways of doing this:

   • On the command line (in a new terminal):

     curl --proxy localhost:8080 http://example.com
     

     The output should contain a <script> element whose first line is // ==UserScript==.

   • In a web browser:

     1. Go to the preferences menu in your web browser, search for proxy and set localhost with port 8080 as HTTP proxy.

     2. Visit http://example.com. You should see a green page and a message saying that Userscript Proxy is working.

On a mobile device

1. You need to know the local IP address of the machine running Userscript Proxy (i.e. where you ran docker run above). This is usually something like 192.168.1.67. You can typically find it by running ip a, ifconfig or ipconfig depending on your operating system.

   If your local IP address is 192.168.1.67, and the proxy is running (see above), this should work:

   curl --proxy 192.168.1.67:8080 http://example.com
   

2. Your mobile device needs to be on the same LAN as your proxy, so make sure it's connected to your Wi-Fi.

3. On your mobile device, go to the settings for the currently active Wi-Fi connection. Find the proxy settings, select Manual proxy or similar, and set 192.168.1.67 with port 8080.

4. Visit http://example.com on your mobile device. You should see the same green page as above.

HTTPS

When you've set up Userscript Proxy on your mobile device as described above, you'll notice that you can't visit sites via HTTPS anymore. This is because your device thinks you're being MITM'd (which, technically, you are – by yourself).

To make HTTPS connections work, you need to tell your device that it should trust your proxy. This is accomplished by installing a certificate.

In general, installing a certificate might pose a security risk. If you don't trust me and mitmproxy, stop here. Otherwise, read on.

1. Stop the proxy by pressing Ctrl + C in the terminal where it's running. Then start it again, this time with the -v flag as shown below:

   docker run -t --rm --name userscript-proxy -p 8080:8080 -v "mitmproxy-ca:/root/.mitmproxy" alling/userscript-proxy
   

   This creates a new Docker volume and mounts it at /root/.mitmproxy, where mitmproxy stores its certificate authority files. This is necessary so that you can restart the proxy later without having to perform all these steps again.

   In this example, mitmproxy-ca is the name of the new Docker volume. You can choose any name you want, as long as it's not already in use.

2. Make sure your mobile device is configured to use the proxy as decribed above.

3. On your mobile device, go to http://mitm.it. You should see icons for Apple, Windows, Android, etc.

4. Click the icon matching your device.

5. Install the certificate.

   Android

   Follow the on-screen instructions. If you're asked to choose between VPN and apps and Wi-Fi, choose VPN and apps.

   iOS

   1. Tap Allow when asked if you want to download a configuration profile.

   2. Open the Settings app and go to General ▶ Profiles.

   3. Under Downloaded profile, tap the mitmproxy profile.

   4. Tap Install three times.

   5. Go back to the main screen in Settings and go to About ▶ Certificate Trust Settings.

   6. Under Enable full trust for root certificates, enable mitmproxy, confirming the action if prompted.

6. You should now be able to browse via HTTPS as usual.

Deploying userscripts

Userscript Proxy comes with one single userscript, useful only for testing that the proxy is up and running. To use userscripts you've downloaded or written yourself, you need to tell Userscript Proxy where they are.

1. You need the absolute path to a directory containing your userscripts. This could be something like /home/alling/userscripts.

2. Run Userscript Proxy like this:

   docker run -t --rm --name userscript-proxy -p 8080:8080 -v "mitmproxy-ca:/root/.mitmproxy" -v "/home/alling/userscripts:/userscripts" alling/userscript-proxy --userscripts-dir "/userscripts"
   

   • -v "/home/alling/userscripts:/userscripts" mounts your userscripts directory at /userscripts inside the Docker container.
   • --userscripts-dir "/userscripts" tells Userscript Proxy to read userscripts from /userscripts.

Apps with certificate pinning

Apps like App Store and Facebook Messenger refuse to connect through a MITM proxy, so their traffic must be ignored by mitmproxy. There are two approaches:

• Blacklisting hosts that cannot connect through the proxy. Tedious, because you have to add exceptions for apps and such all the time.
• Whitelisting hosts where userscripts should be applied. Works well in general, but does not allow universal userscripts that run on all sites, and the whitelist must be updated when a new userscript is added.

Blacklisting or whitelisting is done by giving the --rules flag together with one or more files containing rules. By default, all traffic from hosts matching those rules is ignored (blacklisting); if --intercept is given, matching traffic is instead intercepted (whitelisting).

NOTE: With --transparent, mitmproxy may not be able to see the hostname of responses without intercepting them. In that case, you can only ignore/intercept based on IP address, not hostname.

Examples:

• Take ignore rules from /home/alling/rules/ignore.txt:

  docker run -t --rm -v "/home/alling/rules:/rules" alling/userscript-proxy --rules "/rules/ignore.txt"

• Take intercept rules from all .txt files in the /home/alling/rules directory whose names start with foo:

  docker run -t --rm -v "/home/alling/rules:/rules" alling/userscript-proxy --rules "/rules/foo*.txt" --intercept

Rules can be specified in two ways:

Basic pattern

Based on the syntax used by userscript @include directives. Asterisk (*) means any string (including the empty string). *. is automatically prepended. :* is automatically appended unless the rule contains a colon (:).

To match a domain without matching all of its subdomains, use a regex rule instead (see below).

Examples

Regular expression

If a rule starts and ends with a slash (/), it is treated as a Python regex.

Note that the string to match against contains both a host and a port, e.g. example.com:443, and that the regex is used verbatim (i.e. you have to explicitly provide ^ etc if desired). The only exception is that the case-insensitivity flag (?i) is automatically added.

Also, be careful with $: A regex like /site.com$/ will never match, because it will only be used to check strings like site.com:80.

Anything from a # until the end of the line is treated as a comment. Leading and trailing whitespace have no effect.

Examples

Data usage

Userscript Proxy has no data usage impact when no userscript is injected, i.e. for URLs without any matching userscript. When a script is injected, exactly one of the following things happens:

• The entire userscript is injected as inline JavaScript (potentially dozens or even hundreds of kilobytes).
• A <script> tag referencing the userscript is injected (~100 bytes, depending on the length of the @downloadURL).

A userscript is injected by reference if and only if it has a specified @downloadURL in its metadata. (This can be overridden using the --inline flag, in which case all userscripts are injected inline.)

Userscripts are injected into every response from a matching URL, and the size of a userscript can be anything from a few hundred bytes for the most basic ones to hundreds of kilobytes in extreme cases, so there are massive data usage reductions to be gained from making the userscript accessible by URL and including a @downloadURL. If the @downloadURL approach is not possible, for one reason or the other, it is a good idea to be aware of this issue, and to take appropriate action such as minifying userscripts and adding suitable ignore rules.

Userscript compatibility

Userscript Proxy supports (a subset of) the Greasemonkey metadata syntax. No adaptation of plain JavaScript userscripts should be required. These directives are supported:

• @name
• @version
• @run-at document_(start|end|idle)
• @match
• @include (basic pattern and regex)
• @exclude
• @noframes
• @downloadURL

The GM API and similar runtime facilities are not supported, because userscripts can only be injected as regular scripts.

Options

Options are specified by simply appending them to the docker run command, for example:

docker run -t --rm --name userscript-proxy -p 8080:8080 alling/userscript-proxy --transparent
#          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                         ^^^^^^^^^^^^^
#          flags to `docker run`                                                flags to Userscript Proxy

--bypass-csp ALLOW

Bypass host site's Content Security Policy (if any) to allow userscripts to run properly. If ALLOW is script, the CSP is bypassed only for the userscript itself. Use nothing to never bypass any CSP (meaning userscripts won't work at all on some sites). Use everything to allow everything, which may be necessary if the userscript injects CSS, images etc. Note that the latter completely disables any CSP from every host site into which a userscript is injected. Defaults to script.

--inline, -i

Always inject scripts inline (<script>...</script>), never linked (<script src="..."></script>). Useful to test new userscript features without having to re-upload the userscript and clear browser cache.

--list-injected, -l

Insert an HTML comment in each page specifying which userscripts (if any) were injected.

--no-default-rules

Skip built-in default rules, which are otherwise automatically applied so that common apps like App Store and Facebook Messenger work out of the box.

--no-default-userscripts

Skip loading built-in default userscripts intended for sanity checks and similar purposes, e.g. Example Userscript.

--port PORT, -p PORT

Make mitmproxy listen to TCP port PORT. Defaults to 8080.

Note: Be careful when running Userscript Proxy in Docker! If you want to use e.g. port 1337 on the host machine, do this instead:

docker run -t --rm --name userscript-proxy -p 1337:8080 alling/userscript-proxy

If you really want Userscript Proxy to use a certain port inside the Docker container, e.g. 5555, don't forget to publish that port:

docker run -t --rm --name userscript-proxy -p 1337:5555 alling/userscript-proxy -p 5555

Or you can let the Docker container be a part of the host's network:

docker run -t --rm --network host --name userscript-proxy alling/userscript-proxy -p 5555

--query-param-to-disable PARAM, -q PARAM

Disable userscripts when the request URL contains PARAM as a query parameter. For example, use -q foo to disable userscripts for http://example.com?foo. Defaults to nouserscripts.

--rules FILE

Take ignore or intercept rules from FILE, which can be a glob pattern matching multiple files. By default, matching traffic is ignored; use --intercept to invert this behavior. See examples above.

--transparent, -t

Run mitmproxy in transparent mode. Useful if you cannot set a proxy in the client, e.g. when using OpenVPN Connect on Android to connect to a VPN server on the network where your proxy is running. In such cases, you have to route traffic from the client to the proxy at the network layer instead, making transparent mode necessary.

NOTE: In transparent mode, ignore/intercept rules based on hostname (rather than IP address) may not work, because mitmproxy may not be able to see the hostname of responses without intercepting them.

--userscripts-dir DIR, -u DIR

Load userscripts from directory DIR.

Contribute

How to build and run from source:

git clone https://github.com/SimonAlling/userscript-proxy
cd userscript-proxy
make start