Topic: OpenSSL 3.5.1 forcing TLS 1.3 - need to limit to TLS 1.2

[Mognar]

Hi all,

Hoping to get some assistance with an issue we're running into. So we recently upgraded to Apache 2.4.64 which upgraded OpenSSL from 3.4 to 3.5.1

From all of our testing, it appears that openssl 3.5.1 is forcing TLS1.3 . We are sending mail to an smtp relay server which is limited to TLS1.2 and need to limit openssl to use TLS1.2 but have been unsuccessful.

I reverted the following files back to the OpenSSL 3.4 versions and when done, we're able to send mail without issue, so fairly confident 3.5.1 is the issue:
bin\abs.exe
bin\apr_crypto_openssl-1.dll
bin\libcrypto-3-x64.dll
bin\libssl-3-x64.dll
bin\openssl.exe
modules\mod_ssl.so

If we set SMTPAutoTLS to False, the mail goes through.

We've tried modifying the code, including the following and different variations of the follow:
$mail->SMTPAuth = false;
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
$mail->SMTPAutoTLS = true;
$mail->SMTPOptions = array(
'ssl' => array(
'verify_peer' => true,
'verify_peer_name' => true,
'allow_self_signed' => false,
'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT, // Explicitly force TLS 1.2
)
);

as well as using: $mail->SMTPSecure = 'tlsv1.2';

I've tried modifying the httpd-ssl.conf in the following ways:

1. Changed the ciphersuite directives
2. Tried multiple variations of the following within the vhost block:
SSLProtocol -all +TLSv1.2
SSLProtocol TLSv1.2
3. Tried multiple various of:

# intermediate configuration
SSLProtocol -all +TLSv1.2
SSLOpenSSLConfCmd Curves X25519:prime256v1:secp384r1
SSLCipherSuite ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305
SSLHonorCipherOrder off
SSLSessionTickets off

SSLUseStapling On
SSLStaplingCache "shmcb:logs/ssl_stapling(32768)"

Running s_client -connect relay.xxx.xxx:25 -starttls smtp shows that it negotiated using TLS1.3 and gets a write:errno=10060

Running s_client -connect relay.xxx.xxx:25 -starttls smtp -tls1_2 is successful.

I'm leaving a lot out, but hoping that provides enough info and I'll be happy to provide more if needed. It's been a long week, the pup needs a walk and I need a break from the monitors

So any and all advice would be appreciated at this point.

Thanks in advance!

Mog

[tangent]

Testing locally, with appropriate Apache SSL configuration settings, OpenSSL 3.5.1 (with Apache 2.4.64/65) is able to connect to a web server using TLS 1.2.

Equally, you have proved you can s_client to your SMTP server with TLS 1.2, so this rather shows it's not a problem with OpenSSL 3.5.x libraries per se.

It would appear your problem lies with the PHP code handling the SMTP connection for the PHP mailer, and the likelihood that some function coded into your PHP is no longer available in the updated SSL libraries. Notably, OpenSSL 3.5 has replaced some ageing DES ciphers with AES replacements, which may be relevant to your SMTP connection.

Are you running the latest version of PHP, and if not are you able to update it?

[Mognar]

Hi and thanks for the reply.

I'm the sys admin and this is for one of our supported dept's/servers. I don't handle any of the coding for the site and this is sort of new territory for me, which is why I posted.

This issue is that we need to use smtp servers which we don't manage and are limited to TLS1.2 due to them being on Win 2019. No plans in the near future to upgrade the smtp environment, so we have to be able to connect via 1.2.

PHP is at 8.3.23, so yes, we're current there.

Thanks

[tangent]

I'm no PHP expert, but I don't understand how regressing the various OpenSSL DLL files in Apache affects your PHP SSL backend. I understood that PHP comes with its own OpenSSL library, namely php_openssl.dll (in the ext folder).

This is what I get with default settings on a test instance of PHP:

[Mognar]

Hi Tangent,

Thanks, I really appreciate your help.

The extension is enabled in the php.ini, so yes, you would think that it's using the php_openssl.dll. "extension=openssl"

Here's the code the developer is using:

<?php
require 'vendor/autoload.php'; // Adjust path if needed

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

// Enable verbose debug output
$mail = new PHPMailer(true);
$mail->SMTPSecure = 'TLSv1.2';

try {
// Server settings
$mail->SMTPDebug = 3; // Use 3 for full output
$mail->Debugoutput = 'html'; // Format debug as HTML
$mail->isSMTP();
$mail->Host = 'xxx.xxx.xxx';
//$mail->Host = 'xxx.xxx.xxx';
$mail->Port = 25; // Try 587 if 25 fails
//$mail->Port = 587; // Try 587 if 25 fails
//$mail->SMTPAuth = false;
//$mail->SMTPSecure = false;
//$mail->SMTPAutoTLS = true; // 👈 IMPORTANT: disables STARTTLS attempt

$mail->SMTPAuth = false;
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
$mail->SMTPAutoTLS = true;
$mail->SMTPOptions = array(
'ssl' => array(
'verify_peer' => true,
'verify_peer_name' => true,
'allow_self_signed' => false,
'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT, // Explicitly force TLS 1.2
)
);

//$mail->SMTPOptions = [
// 'ssl' => [
// 'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT,
// 'verify_peer' => false,
// 'verify_peer_name' => false,
// 'allow_self_signed' => true
// ]
//];

//$mail->SMTPAuth = false;
//$mail->SMTPSecure = 'tlsv1.2';
//$mail->SMTPAutoTLS = true;
//
//$mail->SMTPOptions = [
// 'ssl' => [
// 'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT, // Force TLS 1.2
// 'verify_peer' => false,
// 'verify_peer_name' => false,
// 'allow_self_signed' => true,
// ]
//];




// Sender & recipient
$mail->setFrom('xxx@xxx.xxx', 'Email Testing Support');
$mail->addAddress('XXX@xxx'); // Replace with your real email

// Email content
$mail->isHTML(false);
$mail->Subject = 'SMTP Test from PHPMailer';
//$mail->Subject = 'PHP mail Test from PHPMailer';
$mail->Body = "This is a test message to verify SMTP connectivity with xxx.xxx.xxx";
//$mail->Body = "This is a test message to verify PHP mail function with Apache and OSSL";
$mail->send();
echo '<p>Email sent successfully.</p>';
} catch (Exception $e) {
echo '<p style="color:red;"><strong>Mailer Error:</strong> ' . $mail->ErrorInfo . '</p>';

If I didn't mention it prior, if he sets SMTPAutoTLS=False, the mail goes through without issue.

[tangent]

These settings are helpful, and notably, your developer has tried various settings for $mail->SMTPSecure, and $mail->Port numbers, but the one port I'd have expected to see for an SMTPS connection is port 465. Port 25 is the historical non-secure mail service port (and port 587 for STARTTLS).

What I'd do is confirm your SMTP server supports TLS 1.2 on port 465, using the OpenSSL with Apache from a command line, viz:

[Mognar]

Sorry for the late reply, had an injury with the family pet I've been dealing with all week.

I checked and as expected, 465 is no longer active on the relay servers as it's no longer a supported smtp port. (Not RFC compliant)

[tangent]

Ok, so next I'd confirm exactly what level of secure connection your mail server supports when using STARTTLS, i.e.