How do Captcha solving services like 2captcha replicate the recaptcha that a particular user receives by getting the site recaptcha key and the URL of the site.
Also can someone help me understand how to the payload of recaptcha works?
recaptcha payload
Related
Brief Summary
Let's start with a brief introduction of what a Google reCaptcha farm is - a service that bot developers can query via an API to automate solving Google reCaptcha:
The bot is blocked by a Captcha challenge.
It makes an API call to the Captcha farm with the website’s Captcha public key & its domain name as parameters.
The Captcha farm asks one of its workers to solve the Captcha.
After ~30-45 seconds, the Captcha is solved and you obtain its response token.
The bot solves the Captcha by submitting the response token.
In short, solving a Captcha is as simple as calling a function in the bot's code. The attacker doesn't even need to interact directly with the Google reCaptcha by clicking on it. If the attackers know the structure and the URL of the Google reCaptcha callback, i.e. the request where the website sends the Google reCaptcha response token after a successful response has been submitted (which is straightforward by looking at the devtools), they can prove that they've solved a Captcha without even using a real browser.
Problem
My website is fully integrated with Google reCaptcha V2 (Invisible reCaptcha). The implementation follows all steps listed in the documentation. It worked like a charm till now. As time passed by, we experienced different kind of attacks that tried to infiltrate our login. The one the caused the biggest problem was a Dictionary attack combined with automated Google reCaptcha solving mechanism. The attackers are using farms (or may be scripts) that solve the Google reCaptcha and generate unique response codes, which are used by a bot network (different IP addresses around the world, User-Agents, Browser Fingerprints, etc.). Using these codes, the Google reCaptcha is taken out of the picture and we MUST use different mechanisms to block the attackers.
Question
I reviewed the Google reCaptcha documentation multiple times along with different topics related to this problem, but couldn't find a way to prevent such attack in an easy way. I have a few questions and will be very grateful if somebody succeeded to answer them:
Is it possible to bind the Google reCaptcha response code to a code challenge, cookie or something similar in order to ensure that the code is generated by the exact client?
Is there any way to distinguish the Google reCaptcha codes, taken from a farm/script and the ones generated by the exact client?
I found that there are some solutions as DataDome, which are very expensive. Is there something similar but on lower price or an algorithm that can be implemented on my own?
Big thanks in advance!
Script
Below is a simplification of the script that acts like a Google reCaptcha farm:
bypassReCaptcha();
function bypassReCaptcha() {
grecaptcha.render(createPlaceholder(), buildConfiguration());
grecaptcha.execute();
}
function createPlaceholder() {
document.body.innerHTML += '<div class="g-recaptcha-hacker"></div>';
return document.getElementsByClassName('g-recaptcha-hacker')[0];
}
function buildConfiguration() {
return {
size: 'invisible',
badge: 'bottomleft',
sitekey: '<your site-key>',
callback: (reCaptchaResponse) => localStorage.setItem('reCaptchaResponse', reCaptchaResponse)
};
}
I am using a server-side validation - something like this:
curl -X POST 'https://www.google.com/recaptcha/api/siteverify?secret=<your secret>&response=<generated code from above>&remoteip=<client IP address>'
It seems that the remoteip parameter is not working as expected - the validation is successful no matter of the client IP. I checked some topics and seems that this is a common problem:
Google reCAPTCHA's remoteip parameter is ignored
Is there any reason to include the remote ip when using reCaptcha?
I'm currently implementing Google's reCAPTCHA v3 to guard a form. Normally, the way this works is that when a user submits the form, a user response token is generated and conveyed to the back end, which then forwards the token to Google's verification API to get an assessment.
I've found that, for certain attacks, the user response token is missing because the attacker is submitting their POST request to my site directly, rather than using the form. This is good because it makes it obvious that they should be rejected. But I'm wondering if I should go ahead and submit a token-less verification request to Google anyway, knowing that it will fail.
I ask because my understanding is that reCAPTCHA gathers information about my site activity over time, using it to fine tune their assessments. I don't know how this is done, so I don't know if it would be useful to exercise the verification API even when I already know what should be the outcome.
I hope this is the right forum to ask this question.
I've recently integrated reCaptcha v3 into a website I manage in order to protect the login form.
I get alot of noise from users saying that if they are in the office (and originate from the same IP) or customers who are using shared IPS (office IPs) are failing login.
For the meantime I've disabled reCaptcha by allowing score 0 to login.
My question is.. is there a built in way in reCaptcha to send Google's API information about the request or should I just add the reCaptcha score into my own calculation when allowing the login ?
Thanks !
Placement on your website
reCAPTCHA v3 will never interrupt your users, so you can run it whenever you like without affecting
conversion. reCAPTCHA works best when it has the most context about
interactions with your site, which comes from seeing both legitimate
and abusive behavior. For this reason, we recommend including
reCAPTCHA verification on forms or actions as well as in the
background of pages for analytics.
Source: https://developers.google.com/recaptcha/docs/v3
The above document says we need to integrate ReCAPTCHA V3 on multiple pages. So question is, do we really need to generate and verify token for each page or just generating token is enough?
like
grecaptcha.execute(reCaptchaPublicKey, {action: 'cartpage'}).then(function(token) {
//skip verification
});
Note:
On the form for which I want to block the bot, I am generating a token and passing it to the server with the user's form data. Now on the server-side, I am validating token using API and getting a score in response to take further action. like, block the user action if the score is low.
No, Calling grecaptcha.execute with the appropriate action (use 'homepage' for traffic on your homepage) is enough to make the reCAPTCHA service count and process the visit.
The token that is provided to your callback is requested from the reCAPTCHA service by the reCAPCHA client script. Sending it to your server to then send it back to the reCAPTCHA service to get the score makes no sense if you don't use the score.
Google announced Invisible ReCAPTCHA is coming soon. For now, if you want to integrate the new reCAPTCHA to your site or app you can register here.
I do have 2 site keys whitelisted for the new Invisible reCaptcha and I've started "playing" with their examples: see them here https://developers.google.com/recaptcha/docs/invisible
Yes, when the page loads the recaptcha is invisible but when the form is submitted the recaptcha challenge appears all the time. You have to click on images, draw something around something else... etc
I've been testing this on different servers, 2 different sites which have the site key approved to use the Invisible reCaptcha, with different browsers form different locations. Same behavior: Google shows the challenge when the form is submitted on all 3 examples they have on their page.
Is this what we should expect?
Just as with the checkbox, if it can't reliably determine if you aren't a bot, you get a challenge. I can confirm that the invisible part does work when you are detected as a human.
Actually you have to approve the Terms of Service when you create a new reCAPTCHA site, that says that
You agree to explicitly inform visitors to your site that you have implemented the Invisible reCAPTCHA on your site and that their use of the Invisible reCAPTCHA is subject to the Google Privacy Policy and Terms of Use.