Pantheon release notes

Pantheon has updated the default PHP version for the WordPress and WordPress (composer managed) upstreams to PHP 8.3, replacing the previous default of PHP 8.2.

New sites created from these upstreams use PHP 8.3. Existing sites that do not set php_version in their own pantheon.yml move to PHP 8.3 when they apply this upstream update.

Action required

Test the update before you deploy it to the Live environment. Apply it in Dev or a Multidev environment, confirm your plugins and theme work on PHP 8.3, then promote it.

If your site needs to stay on PHP 8.2, pin the version by setting php_version: 8.2 in your site's pantheon.yml before you apply the update. For steps, see Manage PHP Versions.

If you maintain a custom upstream, this change is not reflected in your pantheon.upstream.yml unless you update your fork from Pantheon's upstream.

PHP 8.1 has reached End of Sale on the Pantheon platform. Newly created sites after September 30 2026 will no longer be able set their PHP version to 8.1.

Sites already running PHP 8.1 continue to run. They keep receiving LTS security coverage through PHP Runtime Generation 2, with no action required. A removal date for PHP 8.1 has not been set, and Pantheon guarantees at least 90 days of advance notice before removing any PHP version from the platform.

Action required

If you maintain a custom upstream that sets php_version: 8.1 in pantheon.upstream.yml, update it to a supported version. New sites created from that upstream may otherwise behave unexpectedly on creation.

If your site runs PHP 8.1, plan an upgrade to a recommended PHP version. Pantheon recommends PHP 8.3 or 8.4 for all production sites. For steps, see Upgrade PHP Versions.

Pantheon is beginning the phased migration of Advanced Global CDN (AGCDN) to our next-generation edge platform. Starting September 30, 2026, AGCDN customers whose current configuration is fully supported in Phase 1 are eligible to migrate. Pantheon will contact eligible customers directly.

What's included

Once your migration is complete, you control your edge settings yourself in the Pantheon Dashboard. Changes no longer require a request to Pantheon. Phase 1 controls are configured at the workspace level, apply to every site and environment in the workspace, and are enforced at the edge before requests reach your site.

• IP and CIDR blocking
• Geo blocking
• ASN blocking
• Enterprise WAF
• Image Optimization

How migration works

This migration is not self-serve. Pantheon's Professional Service will:

1. Review your current Legacy AGCDN configuration and confirm feature support with current capabilities on NextGen.
2. Migrate your supported rules and configuration.
3. Make the migrated configuration available for you to review.
4. Coordinate the DNS cutover with you during an agreed change window.
5. Validate the configuration after cutover.

Action required

If you are eligible for Phase 1, you will receive an email. Respond to the ticket to confirm your technical contact so we can schedule your migration.

AGCDN customers who are not contacted for Phase 1 don't need to do anything at this time, and will be contacted at a later date.

Learn more about our switch to Next-generation GCDN with bot protection in this related blog post.

Pantheon is announcing that, as of December 31, 2026, PHP version 7.4 will enter End of Sale. As a result, no new sites can be created with this version after that date.

What happens to existing sites when a PHP version reaches End of Sale?

Existing sites running an end-of-sale PHP version will not be affected. Pantheon will continue to apply security patches for PHP 7.4 where available for the duration of End of Sale.

What to expect going forward

In the future, we expect to transition PHP 7.4 to End of Support status. When this happens, this version will no longer be supported by PHP maintainers, nor will Pantheon provide ongoing updates from our contracted vendors. Customers will assume additional security risk by staying on these versions. Pantheon commits to providing at least 90 days advance notice to customers before transitioning a version of PHP to End of Support.

Action required

If your site is running PHP 7.4, we encourage you to upgrade it to a current PHP version. We recommend PHP 8.3 or 8.4 for all production sites.

For guidance on upgrading, refer to Upgrade PHP Versions.

PHP versions 8.2.34, 8.3.35, 8.4.26, and 8.5.11 are now available on the platform. These updates include important security fixes, along with bug fixes and enhancements that improve performance and stability.

The security fixes include a high-severity issue in the SOAP extension (CVE-2026-91765), plus fixes in OpenSSL certificate verification, the HTTP stream wrapper, and PHP-FPM.

Updates will be applied automatically over the next few days, so no manual action is required. See PHP versions on Pantheon to check or change your site's PHP version.

Starting September 10, 2026, new sites created on Pantheon are provisioned on the next-generation Global CDN, powered by Cloudflare, instead of the legacy Global CDN.

This change applies to newly created sites only. Existing sites are not affected and remain eligible for migration through the normal migration path.

No action is required: the next-generation GCDN is provisioned automatically at site creation.

Advanced Global CDN (AGCDN) customers are not affected by this change. If you have any questions, contact Pantheon Support.

PHP versions 8.4.25 and 8.5.10 are now available on the platform. These updates include bug fixes and enhancements that improve performance and stability. Updates will be applied automatically over the next few days, so no manual action is required.

PHP versions 8.2.33, 8.3.33, 8.4.24, and 8.5.9 are now available on the platform. These releases address three security issues, along with bug fixes and enhancements that improve performance and stability.

The most notable of these is CVE-2026-17543, a high-severity SQL injection in PHP's PostgreSQL extension (ext-pgsql) affecting pg_insert(), pg_update(), pg_select(), and pg_delete(). It is resolved by this update. Only sites using ext-pgsql to connect to an external PostgreSQL database were affected; Pantheon's own MySQL/MariaDB databases are not.

The remaining fixes are an out-of-bounds write in BCMath's bccomp() (CVE-2026-17544, affecting PHP 8.4 and 8.5) and a crash triggered by recursive symlinks in the Phar extension (CVE-2026-7260). PHP 8.5.9 and 8.4.24 also include an updated libgd (CVE-2026-9672).

Updates will be applied automatically over the next few days, so no manual action is required.