README

Challenge/response spam shield for TYPO3 ext:form

What is it?

This TYPO3 extension provides a Challenge/response spam shield for TYPO3 ext:form to prevent automated form submissions.

How does it work?

Challenge/response spam shield adds a hidden input field to every form generated by the TYPO3 form extension. The input field has a precalculated value with a challenge. The included JavaScript will use the challenge to calculate an expected response which will be checked on every form submission. If the expected response is not submitted, validation for the hidden input field is considered as failed and no email will be sent.

In order to make automatic form submissions harder for spambots with active JavaScript, a configurable delay for the JavaScript response calculation can be defined in the extension settings (default value: 3 seconds).

Can the protection be bypassed?

Yes, the challenge/response spam shield can be bypassed, if the algorithm used by the extension is implemented to a spambot. This is however unlikely, since the spambot either has to use JavaScript (which I believe most spambots do not) or has to extract the challenge from the parsed HTML and must calculate and submit the response correctly.

Requirements

The extension uses JavaScript to calculate the expected response, so if JavaScript is disabled on client side, form submission will not be possible.

A modern webbrowser is required to run the JavaScript. Internet Explorer < 11 is not supported.

Installation

Just install the extension on your TYPO3 website using composer or the TYPO3 extension manager. No further configuration is required.

Extension settings

The extension has the following extension settings, which can be adjusted if required. The default values should however be fine for most websites.

crJavaScriptDelay

Defines the delay in seconds for the JavaScript response calculation. The default value is 3 seconds.

minimumPageExpirationTime

If the calculated page cache lifetime if very low (e.g. 60 seconds), it may not be possible to fill out a form before the expiration time for the CR response is reached. This setting defines the minimum amount of second, the calculated page cache lifetime must have. Default value is 900 seconds.

additionalPageExpirationTime

Defines the amount of seconds, which is added to the calculated page cache lifetime, if the calculated page cache lifetime is below the defined value in minimumPageExpirationTime.

obfuscationMethod

Defines the obfuscation method used for the challenge/response calculation. Possible values are:

• 1 - ROT13 (default value)
• 2 - Reverse String

Logging

To log failed requests, it is possible to use a dedicated logfile like shown below:

$GLOBALS['TYPO3_CONF_VARS']['LOG']['Derhansen']['FormCrshield']['writerConfiguration'] = [
    \TYPO3\CMS\Core\Log\LogLevel::DEBUG => [
        \TYPO3\CMS\Core\Log\Writer\FileWriter::class => [
            'logFile' => \TYPO3\CMS\Core\Core\Environment::getVarPath() . '/log/form-crshield.log',
        ]
    ]
];

Usage in own extensions

The extension provides the service ChallengeResponseService which can be used to retrieve and validate the challenge and the expected response. 3rd party extensions can use this service and the included JavaScript snippet to implement the challenge/response protection in their own forms (e.g. Extbase forms).

Versions

Reporting a Vulnerability

Please report vulnerabilities to security@typo3.org.

Extensions using the challenge/response algorithm

The following extensions use the challenge/response algorithm:

• https://github.com/derhansen/form_crshield
• https://github.com/derhansen/powermail_crshield

Thanks for sponsoring

• Thanks to 3m5. Media GmbH for supporting my open source work on this extension