Full Disclosure mailing list archives
Re: Gmail and China's GFW
From: nix () myproxylists com
Date: Tue, 22 Mar 2011 01:44:13 +0200
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/
Current thread:
- Gmail and China's GFW Alien Chatter (Mar 21)
- Re: Gmail and China's GFW bk (Mar 21)
- Re: Gmail and China's GFW Cal Leeming (Mar 22)
- Re: Gmail and China's GFW bk (Mar 21)
- Re: Gmail and China's GFW Cal Leeming (Mar 22)
- Re: Gmail and China's GFW Cal Leeming (Mar 22)
- Re: Gmail and China's GFW bk (Mar 21)
- Re: Gmail and China's GFW Valdis . Kletnieks (Mar 21)
- Re: Gmail and China's GFW nix (Mar 21)
- Re: Gmail and China's GFW nix (Mar 21)
- Re: Gmail and China's GFW bk (Mar 21)
- Re: Gmail and China's GFW nix (Mar 21)
- Re: Gmail and China's GFW Cal Leeming (Mar 22)