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simple robot mitigation module using cookie based challenge/response technique

branch: master
README.markdown

Description

testcookie-nginx-module is a simple robot mitigation module using cookie based challenge/response.

Challenge cookies can be set using different methods:

  • "Set-Cookie" + 302/307 HTTP Location redirect
  • "Set-Cookie" + HTML meta refresh redirect
  • Custom template, JavaScript can be used here.

To prevent automatic parsing, challenge cookie value can be encrypted with AES-128 in CBC mode using custom/random key and iv, and then decrypted at client side with JavaScript.

Directives

testcookie

syntax: testcookie (on|off|var);

default: off

context: http, server, location, if

on - Enable module

off - Disable module

var - Don't intercept requests, only set module variables.

testcookie_name

syntax: testcookie_name <string>

default: TCK

context: http, server, location

Sets cookie name.

testcookie_domain

syntax: testcookie_domain <string>

default: none, set by browser

context: http, server, location

Sets cookie domain.

testcookie_expires

syntax: testcookie_expires <string>

default: 31 Dec 2037 23:55:55 GMT

context: http, server, location

Sets cookie expiration value.

testcookie_path

syntax: testcookie_path <string>

default: /

context: http, server, location

Sets cookie path, useful if you plan to use different keys for locations.

testcookie_secret

syntax: testcookie_secret <string>

default: none

context: http, server, location

Secret string, used in challenge cookie computation, better to be long but static to prevent cookie reset for legitimate users every server restart. If set to "random" - new secret will be generated every server restart, not recomended(all cookies with previous key will be invalid), If not set, only value based on testcookie_session will be used.

testcookie_session

syntax: testcookie_session <variable>

default: required configuration directive

context: http, server, location

Sets the challenge generation function input,

  • $remote_addr - clients IP address will be used as an user unique identifier
  • $remote_addr$http_user_agent - clients IP + User-Agent

testcookie_arg

syntax: testcookie_arg <string>

default: none

context: http, server, location

Sets GET parameter name, used for cookie setting attempts computation,

If not set - server will try to set cookie infinitely.

testcookie_max_attempts

syntax: testcookie_max_attempts <integer>

default: 5

context: http, server, location

Sets maximum number of redirects before user will be sent to fallback URL, according to RFC1945 can't be more than 5.

If set to 0 - server will try to set cookie infinitely(actually, browser will show the error page).

testcookie_p3p

syntax: testcookie_p3p <string>

default: none

context: http, server, location

Sets P3P policy.

testcookie_fallback

syntax: testcookie_fallback <script>

default: none

context: http, server, location

Sets the fallback URL, user will be redirected to after maximum number of attempts, specified by directive testcookie_max_attempts exceded. Nginx scripting variables can be used here. If not set - client will get 403 after max attempts reached.

testcookie_whitelist

syntax: testcookie_whitelist <network list>

default: none

context: http, server

Sets the networks for which the testing will not be used, add search engine networks here. Currently IPv4 CIDR only.

testcookie_redirect_via_refresh

syntax: testcookie_redirect_via_refresh (on|off);

default: off

context: http, server, location

Set cookie and redirect using HTTP meta refresh, required if testcookie_refresh_template used.

testcookie_refresh_template

syntax: testcookie_refresh_template <string>

default: none

context: http, server, location

Use custom html instead of simple HTTP meta refresh, you need to set cookie manually from the template Available all the nginx variables and

$testcookie_nexturl - URL the client should be redirected to, if max_attempts exceeded *testcookie_fallback* value will be here
$testcookie_uid_got - cookie value received from client, empty if no cookie or it does not match format
$testcookie_uid_set - correct cookie value we're expecting from client
$testcookie_ok - user passed test (yes/no)

also, if testcookie_refresh_encrypt_cookie enabled there are three more variables:

$testcookie_enc_key - encryption key (32 hex digits)
$testcookie_enc_iv - encryption iv (32 hex digits)
$testcookie_enc_sec - encrypted cookie value (32 hex digits)

testcookie_deny_keepalive

syntax: testcookie_deny_keepalive (on|off);

default: off

context: http, server, location

Close connection just after setting the cookie, no reason to keep connections with bots.

testcookie_get_only

syntax: testcookie_get_only (on|off);

default: off

context: http, server, location

Process only GET requests, POST requests will be bypassed.

testcookie_https_location

syntax: testcookie_https_location (on|off);

default: off

context: http, server, location

Redirect client to https protocol after setting the cookie, also affects $testcookie_nexturl, useful with 3dparty SSL offload.

testcookie_refresh_encrypt_cookie

syntax: testcookie_refresh_encrypt_cookie (on|off);

default: off

context: http, server, location

Encrypt cookie variable, used with testcookie_refresh_template to force client-side decryption with AES-128 CBC.

testcookie_refresh_encrypt_cookie_key

syntax: testcookie_refresh_encrypt_cookie_key <32 hex digits|random>

default: required directive if encryption enabled

context: http, server, location

Sets encryption key.

Possible values:

random - new key generated every nginx restart
32 hex digits - static key, useful if you plan to obfuscate it deep in client-side javascript.

testcookie_refresh_encrypt_iv

syntax: testcookie_refresh_encrypt_iv <32 hex digits|random|random2>

default: random

context: http, server, location

Sets encryption iv.

Possible values: random - new iv generated for every client request random2 - new iv generated for every nginx restart 32 hex digits - static iv, useful if you plan to obfuscate it deep in client-side javascript

testcookie_internal

syntax: testcookie_internal (on|off);

default: off

context: http, server, location

Process only GET requests, POST requests will be bypassed. Enable testcookie check for internal redirects(disabled by default for optimization purposes!), useful for this type of configs:

rewrite ^/(.*)$ /index.php?$1 last;

Installation

Grab the nginx source code from nginx.org, for example, the version 1.1.15 (see nginx compatibility), and then build the source with this module:

wget 'http://nginx.org/download/nginx-1.1.15.tar.gz'
tar -xzvf nginx-1.1.15.tar.gz
cd nginx-1.1.15/
./configure --add-module=/path/to/testcookie-nginx-module

make
make install

For using client-side cookie decryption, you need to manually grab SlowAES JavaScript AES implementation, patch it(utils/aes.patch) and put it to document root.

Compatibility

Module was tested with nginx 1.1+, but should work with 1.0+.

Example configuration

http {
    #default config, module disabled
    testcookie off;

    #setting cookie name
    testcookie_name BPC;

    #setting secret
    testcookie_secret keepmesecret;

    #setting session key
    testcookie_session $remote_addr;

    #setting argument name
    testcookie_arg ckattempt;

    #setting maximum number of cookie setting attempts
    testcookie_max_attempts 3;

    #setting p3p policy
    testcookie_p3p 'CP="CUR ADM OUR NOR STA NID", policyref="/w3c/p3p.xml"';

    #setting fallback url
    testcookie_fallback http://google.com/cookies.html?backurl=http://$host$request_uri;

    #configuring whitelist
    testcookie_whitelist {
        8.8.8.8/32;
    }


    #setting redirect via html code
    testcookie_redirect_via_refresh on;

    #enable encryption
    testcookie_refresh_encrypt_cookie on;

    #setting encryption key
    testcookie_refresh_encrypt_cookie_key deadbeefdeadbeefdeadbeefdeadbeef;

    #setting encryption iv
    testcookie_refresh_encrypt_cookie_iv deadbeefdeadbeefdeadbeefdeadbeef;

    #setting response template
    testcookie_refresh_template '<html><body>setting cookie...<script type=\"text/javascript\" src=\"/aes.min.js\" ></script><script>function toNumbers(d){var e=[];d.replace(/(..)/g,function(d){e.push(parseInt(d,16))});return e}function toHex(){for(var d=[],d=1==arguments.length&&arguments[0].constructor==Array?arguments[0]:arguments,e="",f=0;f<d.length;f++)e+=(16>d[f]?"0":"")+d[f].toString(16);return e.toLowerCase()}var a=toNumbers("$testcookie_enc_key"),b=toNumbers("$testcookie_enc_iv"),c=toNumbers("$testcookie_enc_set");document.cookie="BPC="+toHex(slowAES.decrypt(c,2,a,b))+"; expires=Thu, 31-Dec-37 23:55:55 GMT; path=/";location.href="$testcookie_nexturl";</script></body></html>';

    server {
        listen 80;
        server_name test.com;


        location = /aes.min.js {
            gzip  on;
            gzip_min_length 1000;
            gzip_types      text/plain;
            root /var/www/public_html;
        }

        location = /w3c/p3p.xml {
            root /var/www/public_html;
        }

        location / {
            #enable module for specific location
            testcookie on;
            proxy_set_header   Host             $host;
            proxy_set_header   X-Real-IP        $remote_addr;
            proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
            proxy_pass http://127.0.0.1:80;
        }
    }
}

See more cases in "docs" directory of the project.

Test suite

This module comes with a Perl-driven test suite. Thanks to the Test::Nginx module in the Perl world.

Sources

Available on github at kyprizel/testcookie-nginx-module.

TODO

  • Code review
  • IPv6 whitelisting
  • More encryption algos (?)
  • Statistics (?)

Bugs

Feel free to report bugs and send patches to kyprizel@gmail.com or using github's issue tracker.

Copyright & License

Copyright (C) 2011-2012 Eldar Zaitov (kyprizel@gmail.com).

All rights reserved.

This module is licenced under the terms of BSD license.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

*   Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
*   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
*   Neither the name of the authors nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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