WordPress Release: 5.5.7

TL;DR

WordPress 5.5.7 is a maintenance release that focuses on developer testing tools and security improvements. It introduces the PHPUnit Polyfills package to improve cross-version testing capabilities and removes an expired DST Root CA X3 certificate to prevent potential SSL verification issues with Let's Encrypt certificates. This release is particularly important for developers working across multiple WordPress versions and for sites using Let's Encrypt SSL certificates with older OpenSSL implementations.

Highlight of the Release

• Introduction of PHPUnit Polyfills package for cross-version testing
• Removal of expired DST Root CA X3 certificate to prevent SSL verification issues
• Improved test infrastructure for developers working with multiple WordPress versions

Migration Guide

No specific migration steps are required for most users upgrading to WordPress 5.5.7.

For developers using the testing infrastructure:

• If you have custom test classes that rely on specific fixture execution order, be aware that the order might change slightly with the new PHPUnit wrappers
• Test classes with code structured as "some code - parent::setUp() call - some more code" in their setUp() method may experience changes in execution order

For site administrators:

• No action is needed regarding the SSL certificate changes; the update automatically removes the expired certificate

Upgrade Recommendations

This release is recommended for all WordPress 5.5.x users, particularly:

1. Developers who work with WordPress testing across multiple versions
2. Sites using Let's Encrypt SSL certificates, especially those on hosting environments with older OpenSSL implementations (1.0.2)

As this is primarily a maintenance and security release, it's advisable to update at your earliest convenience. The changes are focused and targeted, with minimal risk of disruption to existing sites.

Bug Fixes

Test Forward-Compatibility Layer Fix

Fixed an issue with the test wrapper methods introduced in the PHPUnit Polyfills implementation. The initial implementation had a problem where the wrapper methods were not being called due to naming issues. This fix:

• Adds extra camelCase wrappers to the WP_UnitTestCase to call methods in the correct order
• Adds wrappers for the assertPreConditions() and assertPostConditions() fixture methods
• Ensures proper execution order for test fixtures

New Features

PHPUnit Polyfills Package

WordPress 5.5.7 introduces the PHPUnit Polyfills package to the 5.5 branch, making it easier for developers to test their code across multiple WordPress versions. This package provides compatibility layers that allow developers to write tests using modern PHPUnit practices while maintaining backward compatibility.

The update includes:

• Support for both camelCase and snake_case fixture methods in PHPUnit
• Wrappers for modern PHPUnit testing practices
• Infrastructure improvements for cross-branch testing

Security Updates

SSL Certificate Verification Improvement

Removed the DST Root CA X3 certificate that expired on September 30, 2021. This change prevents potential SSL verification issues with Let's Encrypt certificates, particularly on systems using OpenSSL 1.0.2.

The issue affected certificate chain verification where OpenSSL 1.0.2 would prefer a chain leading to the expired DST Root CA X3 certificate, causing SSL verification failures. By removing this expired certificate, WordPress ensures proper SSL verification for sites using Let's Encrypt certificates.

Performance Improvements

No significant performance improvements were included in this release. The changes primarily focus on testing infrastructure and security improvements.

Impact Summary

WordPress 5.5.7 delivers important improvements for developers and site administrators without introducing breaking changes.

For developers, the addition of PHPUnit Polyfills significantly improves the testing experience when working across multiple WordPress versions. This makes it easier to maintain plugins and themes that support a wide range of WordPress installations while using modern testing practices.

For site administrators, the removal of the expired DST Root CA X3 certificate resolves potential SSL verification issues with Let's Encrypt certificates. This is particularly important for sites on hosting environments using older OpenSSL implementations, as it prevents certificate validation failures that could impact site functionality and security.

Overall, this is a targeted maintenance release that addresses specific developer tooling and security needs without requiring significant changes to existing workflows or configurations.