Falcon Media -Magento 2 CSP SRI Lock

Package: falconmedia/magento2-csp-sri-lock
Type: Magento 2 Module
License: MIT
Maintainer: Henk Valk henk@falconmedia.nl

Installation

Via Composer

composer require falconmedia/magento2-csp-sri-lock
php bin/magento module:enable FalconMedia_CspSriLock
php bin/magento setup:upgrade
php bin/magento cache:flush

Verification

After installation, verify that the correct storage class is active:

php bin/magento dev:di:info Magento\Csp\Model\SubresourceIntegrity\Storage\File

Expected output:

Preference: FalconMedia\CspSriLock\Model\SubresourceIntegrity\Storage\File

Issue

Magento 2.4.x stores Subresource Integrity (SRI) hashes in:

pub/static/frontend/sri-hashes.json
pub/static/adminhtml/sri-hashes.json

Under load, multiple PHP-FPM workers can write to the same file simultaneously.

Magento's default implementation writes using file mode 'w' without locking.

This can cause:

• Truncated JSON files
• Partially written content
• Invalid JSON
• Fatal error in checkout:

<!-- -->

Unable to unserialize value. Error: Syntax error
Magento\Csp\Model\SubresourceIntegrityRepository->getData()

This often results in checkout becoming completely unavailable.

Root Cause

The core implementation:

• Opens the file with mode 'w' (truncate immediately)
• Does not use file locking
• Does not use atomic file replacement

If two requests write simultaneously:

Request A → truncates file
Request B → truncates file
Request A → writes partial JSON
Request B → overwrites partially

Result: corrupted JSON → checkout crash.

Solution

This module replaces Magento's default SRI file storage with a safer implementation that:

• Uses flock() for exclusive locking
• Writes to a temporary file first
• Replaces the target using atomic rename()
• Prevents truncated or corrupted JSON
• Keeps full backward compatibility

No database changes.
No configuration required.
Drop-in safe fix.

Testing

1. Remove existing SRI files

rm -f pub/static/frontend/sri-hashes.json
rm -f pub/static/adminhtml/sri-hashes.json
php bin/magento cache:flush

2. Generate concurrent requests

for i in {1..30}; do curl -s https://yourdomain.com/checkout/ > /dev/null & done; wait

3. Validate JSON

php -r 'json_decode(@file_get_contents("pub/static/frontend/sri-hashes.json")); echo json_last_error();'

Expected result:

0

Compatibility

• Magento 2.4.x
• PHP 8.1 / 8.2 / 8.3
• Single-node and multi-node environments

Why This Matters

Checkout outages caused by corrupted SRI files can result in:

• Lost revenue
• Broken storefront
• Emergency hotfixes
• Unnecessary cache clears

This module eliminates that class of failure entirely.

License

MIT License
© 2026 Falcon Media