full-disclosure - Re: Gmail and China's GFW

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <84815087869a68ffe22359d2e482628d.squirrel@gameframe.net>
Date: Tue, 22 Mar 2011 01:44:13 +0200
From: nix@...roxylists.com
To: "Alien Chatter" <feedalienscoffee@...il.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Gmail and China's GFW

> Gmail can be blocked by simply blocking Google's SSL certificate(s).
>
> When you visit Gmail, Google sends your browser its SSL Server
> Certificate. Without this certificate, no connection can be made.
>
> For example, running the following command, then browsing to
> <https://mail.google.com/>, will produce the following output:
>
> $ sudo ngrep -d eth0 -x 'Google Inc'
> ...
>   47 6f 6f 67 6c 65 20 49    6e 63 31 18 30 16 06 03    Google Inc1.0...
>   55 04 03 14 0f 6d 61 69    6c 2e 67 6f 6f 67 6c 65    U....mail.google
>   2e 63 6f 6d 30 81 9f 30    0d 06 09 2a 86 48 86 f7    .com0..0...*.H..
> ...
>
> This output shows part of Google's ASN.1 encoded X.509 certificate.
>
> Therefore, the following Linux firewall commands will stop any
> connection to Gmail:
>
> $ sudo iptables -I INPUT -m string --algo bm --hex-string
> '|476f6f676c6520496e63311830160603550403140f6d61696c2e676f6f676c652e636f6d30819f30|'
> -j DROP
>
> Try it, you will get a connection timeout:
>
> $ curl --connect-timeout 60 https://mail.google.com/
> curl: (28) SSL connection timeout
>
> The same applies for Twitter, Facebook... Much more efficient than
> DNS/IP blocking!
>

Thanks for the information. I was not actually aware of that you can block
with iptables using hex strings. Very nice.

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/