fix(security): prevent XSS vulnerability in initialize() checkout modal

[Olayiwolaaa]

Summary

The initialize() method was interpolating user-supplied values directly
into a <script> block without any escaping, allowing XSS attacks via
any of the customer or customization fields.

Problem

Any field passed to the checkout modal (name, email, title, redirect URL,
etc.) could be used to break out of the JS string context. For example:

• setTitle('</script><script>alert(1)</script>') would inject and execute
  arbitrary JavaScript on the payment page.
• setRedirectUrl('https://evil.com","public_key":"leaked') could leak
  the public key or redirect users to a phishing page.

Changes

Commit 1 — Quick patch: wrapped all interpolated string values with
addslashes() and cast $this->amount to (float) to close the
immediate injection surfaces.

Commit 2 — Proper fix: replaced the entire string-concatenated JS
block with json_encode() using JSON_HEX_TAG | JSON_HEX_QUOT | JSON_THROW_ON_ERROR, which handles all escaping correctly including
</script> injection that addslashes() does not cover.

Also wired up $this->paymentOptions which was set via setPaymentOptions()
but never actually used in the output — it was hardcoded before.

Verification

Manually verified by setting:

->setTitle('</script><script>alert(1)</script>')

Page source confirmed the payload was safely encoded as:

"title":"\u003C\/script\u003E\u003Cscript\u003Ealert(1)\u003C\/script\u003E"

No alert fired. Modal loaded normally.

Testing

• tests/Unit/Checkout/InitializeTest.php covers XSS payloads in
  title, customer name, redirect URL, amount casting, and payment options
• Smoke test available at examples/endpoint/test-initialize.php

Notes

• Discovered a separate bug in setup.php where file_exists('.env')
  uses cwd instead of __DIR__, causing .env not to be found in some
  environments. Submitted as a separate PR: fix: resolve .env loading failure when running under PHP-FPM #97 .

[Abraham-Flutterwave]

Hey @Olayiwolaaa,

Thanks for flagging this! A couple of things before we can move forward:

1. Could you deprecate the initialize() method and redirect the fix to the Modal getHTML method instead?
2. Please also retarget this PR against the dev branch rather than master.

Appreciate the contribution!

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[Olayiwolaaa]

Hey @Olayiwolaaa,

Thanks for flagging this! A couple of things before we can move forward:

1. Could you deprecate the initialize() method and redirect the fix to the Modal getHTML method instead?
2. Please also retarget this PR against the dev branch rather than master.

Appreciate the contribution!

Hi @Abraham-Flutterwave, thanks for the feedback!

1. I've moved the json_encode() XSS fix into Modal::getHtml() and
   marked initialize() as deprecated with a trigger_error pointing users
   to render('inline')->with([...])->getHtml() instead.

2. I've retargeted the PR against dev.

Let me know if anything needs adjusting!

[Abraham-Flutterwave]

Hey @Olayiwolaaa

Please update your test with the ModalEventHandler. see the snippet below:

use Flutterwave\EventHandlers\ModalEventHandler; # add this line 

private function buildInstance(): Flutterwave
    {
        $instance = new Flutterwave();
        $instance
            ->eventHandler(new ModalEventHandler()) # add this line 
            ->setAmount('1000')
            ->setCurrency('NGN')
...

so in src/Flutterwave.php you forgot to use the with($checkoutConfig) before the getHtml() method.

public function initialize(): void
    {
        $checkoutConfig = [
            'public_key'        => self::$config->getPublicKey(),
            'tx_ref'            => $this->txref,
            'amount'            => (float) $this->amount,
            'currency'          => $this->currency,
            'country'           => $this->country,
            'payment_options'   => $this->paymentOptions,
            'redirect_url'      => $this->redirectUrl,
            'first_name'        => $this->customerFirstname,
            'last_name'         => $this->customerLastname,
            'email'             => $this->customerEmail,
            'phone_number'      => $this->customerPhone,
            'payment_method'    => $this->paymentOptions,
            'customizations'    => [
                'title'         => $this->customTitle,
                'description'   => $this->customDescription,
                'logo'          => $this->customLogo,
            ],
        ];
        ...

        echo $this->render(Modal::POPUP)->with($checkoutConfig)->getHtml();
  }

Please run the command ./vendor/bin/pest --filter "InitializeTest" to test and ensure backward compatibility of the initialize method.

thanks

[Abraham-Flutterwave]

FYA @Olayiwolaaa #96 (comment)

[Olayiwolaaa]

FYA @Olayiwolaaa #96 (comment)

Hey @Abraham-Flutterwave
Fixes XSS vulnerabilities in the initialize() method by ensuring all
user-supplied values are properly escaped in the rendered checkout modal HTML.

Changes:

src/Flutterwave.php

• Restructured $checkoutConfig in initialize() to pass fields at the
  top level (email, phone_number, first_name, last_name, payment_method)
  to match the contract expected by Modal::with()
• Customizations (title, description, logo) now flow through to the modal output

src/Library/Modal.php

• Added JSON_HEX_APOS flag to escape single quotes in JSON output
• Added JSON_PRESERVE_ZERO_FRACTION to preserve float formatting (e.g. 100.0)
• Customization values are set on the payload and included in the checkout config JSON

tests/Unit/Checkout/InitializeTest.php

• Fixed testInitializeEscapesScriptTagInTitle assertion to not match
  legitimate </script><script> in the HTML template
• Rewrote testInitializeIsDeprecated to use set_error_handler since
  @trigger_error suppresses PHPUnit's deprecation exception conversion

Testing

All 6 tests in tests/Unit/Checkout/InitializeTest.php pass.