cross-posted from: https://infosec.pub/post/11021006

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TLS-encumbered captive portal (transit service)

A transit service offered wi-fi but the network forcibly redirected me to a captive portal that triggers this error:

net::ERR_SSL_VERSION_OR_CIPHER_MISMATCH

I tried a couple browsers and tried rewriting the https:// scheme as http:// but SSL redirect was forced consistently. The error apparently implies my phone’s browser can’t do TLS 1.3.

It seems like a shitty move for a transit service to require passengers to use TLS 1.3 just to tick a fucking box that says “I agree” (to the terms no one reads anyway). Couple questions:

  • I’m generally in the /protect everything by default/ school of thought. But I cannot get my head around why a captive portal where people just tap “I agree” would warrant disclosure protection that could hinder availability. In reality, I don’t really know what the captive portal at hand requests… maybe it demands people’s phone# or email, in which case it might make sense (though I would object to them collecting that info in a GDPR region in the 1st place).

  • Is there a good reason for a captive portal to require TLS 1.3? It seems either the network provider does not trust their own network, or they’re simply incompetent (assumes everyone runs the latest phones). But if I’m missing something I would like to understand it.

I still have to investigate what limitation my browser has and whether I can update this whilst being trapped on an unrooted Android 5.

Bypass methods

I guess I need to study:

  • ICMP tunnel (slow, but IIUC it’s the least commonly blocked)
  • SSH tunnel
  • others?

Are there any decent FOSS tools that implement the client side of tunnels without needing root? I have openvpn but have not tested to see if that can circumvent captive portals. I’ve only found:

  • MultiVNC - VNC over SSH
  • AVNC - VNC over SSH
  • ConnectBot - Can all traffic be routed over this SSH tunnel, or just a shell session?
  • VX ConnectBot - same as connectBot but expanded

I’m curious if the VNC clients would work but at the same time I’m not keen to bring in the complexity of then having to find a VNC server. Running my own server at home is not an option.

My to-do list of things to tinker with so far:

Legal options

If a supplier advertises Wi-Fi but then they render it dysfunctional by imposing arbitrary tech requirements after consumers have already bought the product/service it was included with (coffee, train/bus/plane fare, etc), then they neglect to support it, doesn’t that constitute false advertising? Guess this is out of scope for the community but I might be ½ tempted to file false advertising claims with consumer protection agencies in some cases.

And when a captive portal demands email or phone number, it would seem to be a GDPR violation. Some public libraries make wi-fi access conditional on sharing a mobile phone number which then entails an SMS verification loop.