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[Captive-portals] Use Case: "Carrier Grade Captive Portal"
I visited the capport WG the first time in Chicago. Thank you very much for
the presentations! Afterwards I had a very brief chat with Martin about a use
case, I name “carrier grade captive portals”. As a result I want to present
this use case to you on this mailing list:
*Background and use case:*
In Germany the Federal Office for Information Security informs the ISPs with
IPs, timestamp and other information of users that are part of a botnet. The
ISPs are informing the users about the infection. We can not inform the users
without the help of the ISP as they are the only ones knowing who is behind
the dynamic IP address users get normally in Germany.
There are different ways to inform users by the ISPs: e-mail, snail mail or a
carrier grade captive portal (aka walled garden, forced portal),
The most efficient way to inform and get systems cleaned has been proven is
the carrier grade captive portal.
One of the internet service providers, NetCologne, uses a, as they call it,
Forced Portal. The current solution is legal in germany, if the ISPs terms of
service are appropriate.
*Technically it roughly works like this:*
- When the abuse management system detects that a user is infected, the CPE
customers router connection (PPOE connection) is disconnected and immediately
a new PPOE connection is started.
- With the new PPOE connection, the CPE customers router gets a new DNSServer,
IP, gateway (policy routing) and is connected to a carrier grade captive
- Within the new network connection all traffic is routed through a HTTP/HTTPS
proxy. This proxy allows the user to access selected sites like informational
sites about infections, AV and OS vendors and will otherwise present an
information page to the user. This information page tells the user about the
situation, including information about the infection(s) and instructs him how
to clean the system.
*Problem (almost the same as you know it):*
As with captive portals in local networks this worked pretty well using HTTP.
Also on Browsers, which first tries a HTTP connection, the information
page is displayed. Problem occurs now with HTTPS. Especially Google Chrome
does no longer connect first using HTTP when the user enters a domain name of
a web page if using HSTS and HSTS preload.
Connecting with HTTPS, the browser detects a MITM attack (which of course
makes sense, because it is MITM) and does not display the information page.
Instead an error page is displayed, which generates a whole lot of calls to
the costumer support. An addional problem we encounter is that the well known
detection strategies used by iOS/macOS, Windows and Android for captive
portals do *never* work in our case.
Reason is that these detection strategies will only test for captive portals,
when the network connection of the actual device (for example using WiFi) is
started new. In our case the customers CPE router gets a new PPPOE
connection, but the client does not detect that the network connection to
the internet was dropped by the router.
Do you think that „carrier grade captive portals“ are in scope of the capport
WG charta? Would the work already done at capport help to cope with this
My understanding of the current work in capport is, that it will not solve
this problem entirely, but I think, it may already be half-way towards a
solution. Because pushing a customer to a walled garden does not do a status
change on the client system, but the CPE might work as some kind of “captive
portal relais”, using at least parts of the current architecture of capport
on the internal LAN.
Do you think it is usful that the capport WG considers our use case in its
work? Any help is appreciated.
Referat CK 15
Federal Office for Information Security (BSI)
Godesberger Allee 185 -189
Telefon: +49 228 99 9582-5955
Fax: +49 228 99 10 9582-5955
E-Mail: [email protected]