psiphon-tunnel-core/MobileLibrary/iOS/SampleApps/TunneledWebView

iOS Library Sample App: TunneledWebView

Tunneling UIWebView

Note: this approach does not work with WKWebView (see http://www.openradar.me/17190141).

This app tunnels UIWebView traffic by proxying requests through the local Psiphon proxies created by PsiphonTunnel. The listening Psiphon proxy ports can be obtained via TunneledAppDelegate delegate callbacks (see onListeningSocksProxyPort and onListeningHttpProxyPort in AppDelegate.swift).

This is accomplished by registering NSURLProtocol subclass JAHPAuthenticatingHTTPProtocol with NSURLProtocol. JAHPAuthenticatingHTTPProtocol is then configured to use the local Psiphon proxies. This is done by setting the connectionProxyDictionary of NSURLSessionConfiguration. See + (JAHPQNSURLSessionDemux *)sharedDemux in JAHPAuthenticatingHTTPProtocol.m.

We use a slightly modified version of JiveAuthenticatingProtocol (https://github.com/jivesoftware/JiveAuthenticatingHTTPProtocol), which in turn is largely based on Apple's CustomHTTPProtocol example.

*** Caveats ***

i18n API Leaks Timezone

The Internationalization API (i18n) provides websites, though a JavaScript API, with access to the timezone used by the user's browser (in this case UIWebView). This does not reveal the precise location of the user, but can be accurate enough to identify the city in which the user is located.

Like the "Untunneled WebRTC" issue mentioned below, the i18n API cannot be disabled without disabling JavaScript.

NSURLProtocol Challenges

NSURLProtocol is only partially supported by UIWebView (https://bugs.webkit.org/show_bug.cgi?id=138169) and iOS, meaning that some network requests are made out of process and are consequently untunneled.

Below we address the exceptions we have encountered, but there may be more.

Untunneled Media

In some versions of iOS audio and video are fetched out of process in mediaserverd and therefore are not intercepted by NSURLProtocol.

In our limited testing iOS 9/10 leak and iOS 11 does not leak.

Workarounds

It is worth noting that this fix is inexact and may not always work. If one has control over the HTML being rendered and resources being fetched with XHR it is preferable to alter the media source URLs directly beforehand instead of relying on the javascript injection trick.

*This is a description of a workaround used in the Psiphon Browser iOS app and not of what is implemented in TunneledWebView. TunneledWebView does NOT attempt to tunnel all audio/video content in UIWebView. This is only a hack which allows tunneling audio and video in UIWebView on versions of iOS which fetch audio/video out of process.*

Background

In PsiphonBrowser we have implemented a workaround for audio and video being fetched out of process.

PsiphonTunnel's HTTP Proxy also offers a "URL proxy (reverse proxy)" mode that relays requests for HTTP or HTTPS or URLs specified in the proxy request path.

This reverse proxy can be used by constructing a URL such as http://127.0.0.1:<proxy-port>/tunneled-rewrite/<origin media URL>?m3u8=true.

When the retrieved resource is detected to be a M3U8 playlist a rewriting rule is applied to ensure all the URL entries are rewritten to use the same reverse proxy. Otherwise it will be returned unmodified.

Fix

• Media element URLs are rewritten to use the URL proxy (reverse proxy).
• This is done by injecting javascript into the HTML as it is being loaded which rewrites media URLs to use the URL proxy (reverse proxy).
• If a CSP is found in the header of the response, we need to modify it to allow our injected javascript to run.
  • This is done by modifying the CSP to include a nonce generated for our injected javascript, which is included in the script tag.

Requests to localhost (127.0.0.1) should be excluded from being proxied so the system does not attempt to proxy loading the rewritten URLs. They will be correctly proxied through PsiphonTunnel's reverse proxy.

Untunneled OCSP Requests

See "Online Certificate Status Protocol (OCSP) Leaks" in ../../USAGE.md.

Untunneled WebRTC

WebRTC in UIWebView does not follow NSURLProtocol and cannot be disabled without disabling JavaScript. If not disabled, WebRTC will leak the untunneled client IP address and the WebRTC connection may be performed entirely outside of the tunnel.

One solution would be to use a WebRTC library which allows setting a proxy; or allows all requests to be intercepted, and subsequently proxied, through NSURLProtocol.

More details can be found in this issue: https://github.com/OnionBrowser/OnionBrowser/issues/117.

Configuring, Building, Running

The sample app requires some extra files and configuration before building.

Get the framework.

1. Run pod install

Get the configuration.

1. Contact Psiphon Inc. to obtain configuration values to use in your app. (This is requried to use the Psiphon network.)
2. Make a copy of TunneledWebView/psiphon-config.json.stub, removing the .stub extension.
3. Edit psiphon-config.json. Remove the comments and fill in the values with those received from Psiphon Inc. The "ClientVersion" value is up to you.

Ready!

TunneledWebView should now compile and run.

Loading different URLs

Just update urlString = "https://freegeoip.net" in onConnected to load a different URL into UIWebView with TunneledWebView.

License

See the LICENSE file.