Automatic mode of obfuscation does not work properly on certain networks

[mullbird]

Is it a bug?

• I know this is an issue with the app, and contacting Mullvad support is not relevant.

I have checked if others have reported this already

• I have checked the issue tracker to see if others have reported similar issues.

Current Behavior

In Japan, there is a membership-based public wireless LAN service called Wi2 (AS111360).

This wireless LAN hotspot uses a special communication control not often seen elsewhere to interfere with the use of Wireguard. It appears to successfully connect to the Wireguard tunnel, but it is not possible to upload within the tunnel. Downloading and pinging can be performed within the tunnel. This inexplicable communication control is taking place regardless of the Wireguard port number.

Expected Behavior

This communication control can be circumvented by using UDP-over-TCP.

However, if the obfuscation setting is set to automatic in the Mullvad app, the connection is made without obfuscation, even though UDP-over-TCP should be enabled. As a result, the user must manually enable UDP-over-TCP.

Is it possible to improve the Mullvad app to detect the communication control and enable UDP-over-TCP automatically? A possible approach would be to connect once, test the TCP upload, and if the upload fails, enable UDP-over-TCP and reconnect.

Steps to Reproduce

1. Connect to Wi2 installed at Starbucks
2. Make Wireguard connections
3. Perform an Ookla speed test

Failure Logs

Android version

15

Device model

Pixel 7 Pro

Mullvad VPN app version

2024.10-beta2

Additional Information

• This problem may not apply to all Wi2 access points, but only to Wi2 installed at Starbucks.
• This problem may apply not only to Wireguard, but also to UDP OpenVPN. This problem does not affect TCP OpenVPN.

[mullbird]

Twitter posts that may have something to do with this issue

スタバのKDDI(Wi2)系のWi-Fi、VPN接続した後にTCP/UDP 3389な通信は流れるようになったけど、TCP 80/443な通信が流れないのマジで謎。
MTU値の問題かと思ったけど違うようで分けらからん。。。。
https://x.com/harkas_jp/status/1330381819125043207

おっと。スタバはOpenVPNのUDPはブロックしているんですね💦
https://x.com/__snow_rabbit__/status/1377093266659676161

そもそも社内ネットワークに入るためのVPNがスタバの野良WiFiだと通らない気がするけど、通るのかな
openvpnとwireguardがスタバの野良WiFi使えないのは確認した
https://x.com/4TZLaxhuOzKxB5/status/1805491885860950337