PayPal IPN security VERIFIED

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3 Answers

paypalsecurity
90%

Your mistake is on step 3; you're sending the data back to PayPal via HTTPS (to https://www.paypal.com/cgi-bin/webscr?cmd=_notify-validate to be precise) and PayPal sends a HTTP response on the same (SSL secured) connection with an INVALID/VERIFIED response. As long as you ensure you validate the SSL certificate presented to you, you can rest assured the data is genuine if you receive a 'VERIFIED' response. ,PayPal answers INVALID with http (not https) so hacker can change it again on VERIFIED. Hacker gets profit.,receive a data from PayPal on our http://my-magazine.com/process_pp.php This data is not encrypted because my site is on http. Am I right? So (if it's not encrypted) some hacker can change it., Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers

Incidentally, the default IPN (PHP) sample code forces certificate and cn validation;

curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
88%

You must send these IPN variables back to PayPal servers for verification. Upon verification, PayPal will send a response string with "VERIFIED" or "INVALID".,If your server consistently fails to respond, your IPN may be disabled, in which case you will receive an notification on your primary paypal email address.,You will receive the transaction-related IPN variables on your IPN url that you have specified in your request, otherwise it will default to the IPN url set in your PayPal account.,If your server fails to respond with a successful HTTP response (200), PayPal will resend this IPN either until a success is received or up to 16 times.

Update IPN postback URLs in google script
72%

PayPal IPN sends a POST request with a variable number of fields to the notify URL, in order to confirm that the POST request is legit we need to resubmit the same request along with a additional cmd=_notify-validate field to PayPal, which then replies VERIFIED or INVALID.,bad person replies VERIFIED, receives goods as if they had paid.,My question is, why do we need to resend the request to PayPal? Wouldn't something like this suffice?,IMPORTANT: PayPal expects to receive a response to an IPN message within 30 seconds.

My question is, why do we need to resend the request to PayPal? Wouldn't something like this suffice?

if (preg_match('~^(?:.+[.])?paypal[.]com$~i', gethostbyaddr($_SERVER['REMOTE_ADDR'])) > 0) {
   // request came from PayPal, it's legit.
}
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