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Canary: Input Detection and Response

The origin of the term "canary" (as a method of detection) was originally used by those that worked deep in mines and would take a canary (the bird) with them to detect gas or other reasons they needed to leave. If the bird started behaving oddly they knew something was amiss. This same concept is applied in the security world and is similarly called a "canary".

Similarly, the Canary library allows you to define key/value combinations that can be used to detect when certain data is used and notify you using a variety of methods including the default PHP error log, log handling via Monolog and messages to Slack channels.

For example, you may generate a special username that you want to use as a trigger. This username isn't actually a user in your system but you do want to be notified if a login attempt is made using it. Canary makes this simple by defining checks with an if method and, optionally, a handler using a then method. For example, say we generated the username of canary1234@foo.com and we want to detect when it's used. You can define this in a Canary expression like so:

<?php
$_POST = [
    'username' => 'canary1234@foo.com',
    'password' => 'sup3rs3cr3t'
];

\Psecio\Canary\Instance::build()->if('username', 'canary1234@foo.com')->execute();

// Or you can set multiple match values to look for with an array
$matches = [
    'username' => 'canary1234@foo.com',
    'password' => 'sup3rs3cr3t'
];
\Psecio\Canary\Instance::build()->if($matches)->execute();
?>

In this example we're looking at the current input and checking to see if there's a username value of canary1234@foo.com. In the case of our current $_POST values, there's a match. By default (if no then handler is defined) the information about the match is output to the error like (via the Psecio\Canary\Notify\ErrorLog handler). The JSON encoded result looks like this:

{"type":"equals","key":"username","value":"canary1234@foo.com"}

NOTE: Canary automatically pulls in the $_GET and $_POST superglobal values for evaluation so you don't need to manually pass then in.

Using an external data source

Canary also allows you to use a (static) class method to provide the if portion of the evaluation with data. To use it, just pass in the class and static method name as a string:

<?php
$classMethod = '\Foo\Bar::criteria';

\Psecio\Canary\Instance::build()->if($classMethod)->execute();
?>

The return from this method must be an array otherwise an exception will be thrown.

Supported Notifier Methods

Currently Canary supports the following notification methods:

Creating a Custom Handler (Callback)

If you don't want your results to go to the error log, you can create your own handler via the then method. Currently the only custom handler supported is a callable method. So, say we wanted to output a message to the user of our special username and kill the script. We might use something like this:

<?php
$_POST = ['username' => 'canary1234@foo.com'];

\Psecio\Canary\Instance::build()->if('username', 'canary1234@foo.com')
    ->then(function($criteria) {
        die("You shouldn't have done that!");
    })
    ->execute();
?>

In this handler, when it detects that the username value matches our criteria, the callback is executed and the die call kills the script.

Passing in custom data

You can also provide your own data set if you don't want to auto-load the current $_GET and $_POST values. To pass the data in you can use the data value in the configuration and passing it in:

<?php
$config = ['data' => [
    'username' => 'foobar@baz.com'
]];
\Psecio\Canary\Instance::build($config)->if('username', 'canary1234@foo.com')->execute();
?>

Using a default logger

You can set it as the default logger for all if checks via the notify key in the build() configuration options:

<?php

// create a log channel
$log = new Logger('name');
$log->pushHandler(new StreamHandler('/tmp/mylog.log', Logger::WARNING));

$config = [
    'notify' => $log
];
\Psecio\Canary\Instance::build($config)->if('username', 'canary1234@foo.com')->execute();

?>

NOTE: If you provide a default handler via the notify configuration it will override all other custom notification methods.

Using Monolog

The Canary tool also allows you to use the Monolog logging library to define a bit more customization to the structure of the data and how it's output. Like before, we create the Canary instance but for the input of the then method we provide a Monolog\Logger instance:

<?php
use Monolog\Logger;
use Monolog\Handler\StreamHandler;

require_once 'vendor/autoload.php';

$_GET = ['username' => 'test'];

// create a log channel
$log = new Logger('name');
$log->pushHandler(new StreamHandler('/tmp/mylog.log', Logger::WARNING));

\Psecio\Canary\Instance::build()
    ->if('username', 'canary1234@foo.com')
    ->then($log)
    ->execute();
?>

Using Slack

You can also make use of the Maknz\Slack library to send messages to Slack when a canary is triggered:

<?php
$settings = [
	'channel' => '#my-channel-name',
	'link_names' => true
];
$slack = new Maknz\Slack\Client('https://hooks.slack.com/services/.....', $settings);

\Psecio\Canary\Instance::build($config)->if('username', 'canary1234@foo.com')->then($slack);
?>

You'll need to set up an incoming webhook and replace the URL value in the Client create with the custom URL you're given. The default name for the notifications is Canary Agent and the output includes the same JSON information as the other notification methods.

Using PagerDuty

Canary also allows you to send notifications to your account on the PagerDuty service using the nmcquay/pagerduty library:

<?php
$pager = new \PagerDuty\Event();
$pager->setServiceKey('[.... your service ID ....]');

\Psecio\Canary\Instance::build($config)->if('username', 'canary1234@foo.com')->then($pager);
?>

You can find the service ID by going to your services page (https://[your domain].pagerduty.com/services) and clicking on the service you want to use. The ID is under the "Integrations" tab as the "Integration Key".