Security Advisory: Malicious Activity Affecting Platform Hosts

What to do

• Check whether you use Pantheon Customer Sites in us. Check your stack

  Paste a package.json, lockfile, Terraform or a list of domains at down.guide/stack to see every provider you depend on.

• Confirm your retries, queues and scheduled jobs caught up after the 5d 2h it lasted.

  Anything that failed between 2026-10-01 19:38 UTC and 2026-10-06 22:21 UTC may need a replay.

• Subscribe to Pantheon's feed to hear about the next one first. RSS feed

  https://down.guide/feed?provider=pantheon works in Slack (/feed subscribe), Discord feed bots and any RSS reader.

Updates from Pantheon 5

1. monitoringOct 1, 2026, 7:38 PM UTC

   Beginning September 29, Pantheon identified malicious activity in which an attacker gained control of a customer website and used it to target platform resources. Activity from the compromised site attempted to exploit a Linux kernel vulnerability (CVE-2026-53362) on platform application hosts, and some sites may have briefly experienced interruptions as a result. We have taken the following actions: - Disabled and deleted the affected site. - Accelerated the operating-system and kernel updates already in progress, bringing application hosts to a version that addresses this vulnerability. - Deployed additional platform protections and monitoring. We have notified the affected customer directly. The compromise was limited to that single site; based on the information available to us, we have found no evidence of platform-wide data exfiltration or that this activity exposed data belonging to other customers. We are continuing to review platform activity and will update this advisory if that changes. How to protect your site: Attackers most often gain control of a site through outdated or unmaintained code. Keeping your site current is the most effective protection. We strongly encourage all customers to keep CMS core, plugins, and themes fully updated, remove and delete sites and code you no longer use, and review user and credential access. If you notice unexpected code, deployments, or changes on your site, contact Pantheon Support. We will post updates here as more information becomes available. If you have questions, please contact Pantheon Support.

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2. monitoringOct 2, 2026, 3:05 PM UTC

   As our investigation has continued, we have determined that a small number of customer sites — not one — were affected. In each case, the site was first compromised through a weakness in its own application, then used to interact with platform services. We are working directly with the affected customers on cleanup and credential rotation, and we have added platform controls to restrict this activity and detection to identify it going forward. The activity remains limited to the individual affected sites and their own data. We have found no evidence that any other customer's site or data was accessed. What you can do: Keeping your site current is the most effective protection. Please update your CMS core, plugins, themes, and modules to the latest versions; remove plugins, themes, and modules you don't use; and delete sites you no longer need. If you notice unexpected code, deployments, or changes on your site, contact Pantheon Support. We will continue to post updates here.

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3. monitoringOct 3, 2026, 4:29 PM UTC

   We are continuing to monitor and work through the remaining remediation and hardening. Our initial response is complete, and we are now working directly with the affected customers on site cleanup and credential rotation. We have added further protections and monitoring to help prevent and detect this type of activity. Based on the information available to us, we have found no evidence that any other customer's site or data was accessed. We will share another update as the remaining work progresses. As a reminder, the most effective protection is keeping your site current: please keep your CMS, plugins, themes, and modules up to date, remove anything you no longer use, review your user and credential access, and contact Pantheon Support if you notice unexpected code, deployments, or other changes on your site.

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4. monitoringOct 5, 2026, 6:08 PM UTC

   Remediation and platform hardening remain ongoing. We are continuing to monitor systems closely while working directly with affected customers.

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5. resolvedOct 6, 2026, 10:21 PM UTC

   This incident has been resolved.

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Corrections

None so far.

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