SSL error SSL3_GET_SERVER_CERTIFICATE:certificate verify failed

The file that you downloaded (http://curl.haxx.se/ca/cacert.pem) is a bundle of the root certificates from the major trusted certificate authorities. You said that the remote host has a self-signed SSL certificate, so it didn't use a trusted certificate. The openssl.cafile setting needs to point to the CA certificate that was used to sign the SSL certificate on the remote host. PHP 5.6 has been improved over previous versions of PHP to now verify peer certificates and host names by default (http://php.net/manual/en/migration56.openssl.php)

You'll need to locate the CA certificate that was generated on the server that signed the SSL certificate and copy it to this server. If you're using self-signed certificates, you'll need to add the CA cert that was used to sign the remote host's SSL certificate to the trusted store on the server you're connecting from OR use stream contexts to use that certificate for each individual request. Adding it to the trusted certificates is the simplest solution. Just add the contents of the remote host's CA cert to the end of the cacert.pem file you downloaded.

Previous:

fsockopen doesn't support stream contexts, so use stream_socket_client instead. It returns a resource that can be used with all the commands that fsockopen resources can.

This should be a drop in replacement for the snippet you have in your question:

<?php

$contextOptions = array(
    'ssl' => array(
        'verify_peer' => true, // You could skip all of the trouble by changing this to false, but it's WAY uncool for security reasons.
        'cafile' => '/etc/ssl/certs/cacert.pem',
        'CN_match' => 'example.com', // Change this to your certificates Common Name (or just comment this line out if not needed)
        'ciphers' => 'HIGH:!SSLv2:!SSLv3',
        'disable_compression' => true,
    )
);

$context = stream_context_create($contextOptions);

$fp = stream_socket_client("tcp://{$host}:{$port}", $errno, $errstr, 20, STREAM_CLIENT_CONNECT, $context);

if (!$fp) {

    echo "$errstr ({$errno})<br />\n";

}else{
    
    $this->request = 'POST '.substr($this->url, strlen($this->host)).' HTTP/1.1'.$crlf
        .'Host: '.$this->host.$crlf
        .'Content-Length: '.$content_length.$crlf
        .'Connection: Close'.$crlf.$crlf
        .$body;

    fwrite($fp, $this->request);

    while (!feof($fp)) {
        $this->response .= fgets($fp);
    }

    fclose($fp);

}

I faced a similar issue during work with Ubuntu 16.04 by using Docker. In my case that was a problem with Composer, but error message (and thus the problem) was the same.

Because of minimalist Docker-oriented base image I had missing ca-certificates package and simple apt-get install ca-certificates helped me.

Add

$mail->SMTPOptions = array(
'ssl' => array(
    'verify_peer' => false,
    'verify_peer_name' => false,
    'allow_self_signed' => true
));

before

mail->send()

and replace

require "mailer/class.phpmailer.php";

with

require "mailer/PHPMailerAutoload.php";

The problem is in new PHP Version in macOS Sierra

Please add

stream_context_set_option($ctx, 'ssl', 'verify_peer', false);

In my case, I was on CentOS 7 and my php installation was pointing to a certificate that was being generated through update-ca-trust. The symlink was /etc/pki/tls/cert.pem pointing to /etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem. This was just a test server and I wanted my self signed cert to work properly. So in my case...

# My root ca-trust folder was here. I coped the .crt file to this location
# and renamed it to a .pem
/etc/pki/ca-trust/source/anchors/self-signed-cert.pem

# Then run this command and it will regenerate the certs for you and
# include your self signed cert file.
update-ca-trust

Then some of my api calls started working as my cert was now trusted. Also if your ca-trust gets updated through yum or something, this will rebuild your root certificates and still include your self signed cert. Run man update-ca-trust for more info on what to do and how to do it. :)

Firstable, make sure that you Antivirus software doesn't block SSL2. Because I could not solve a problem for a long time and only disabling the antivirus helped me

You mention the certificate is self-signed (by you)? Then you have two choices:

add the certificate to your trust store (fetching cacert.pem from cURL website won't do anything, since it's self-signed)

don't bother verifying the certificate: you trust yourself, don't you?

Here's a list of SSL context options in PHP: https://secure.php.net/manual/en/context.ssl.php

Set allow_self_signed if you import your certificate into your trust store, or set verify_peer to false to skip verification.

The reason why we trust a specific certificate is because we trust its issuer. Since your certificate is self-signed, no client will trust the certificate as the signer (you) is not trusted. If you created your own CA when signing the certificate, you can add the CA to your trust store. If your certificate doesn't contain any CA, then you can't expect anyone to connect to your server.

If you are using macOS sierra there is a update in PHP version. you need to have Entrust.net Certificate Authority (2048) file added to the PHP code. more info check accepted answer here Push Notification in PHP using PEM file

Have you tried using the stream_context_set_option() method ?

$context = stream_context_create();
$result = stream_context_set_option($context, 'ssl', 'local_cert', '/etc/ssl/certs/cacert.pem');
$fp = fsockopen($host, $port, $errno, $errstr, 20, $context);

In addition, try file_get_contents() for the pem file, to make sure you have permissions to access it, and make sure the host name matches the certificate.