Read-only Actions cache for untrusted triggers

GitHub Actions now issues read-only cache tokens to the default branch for workflow events that can be triggered without write permissions to the repository. This applies least privilege to the cache and prevents common privilege-escalation paths through cache poisoning.

Previously, the Actions service issued read-write cache tokens for every workflow event, including triggers like pull_request_target, issue_comment, and fork-pull-request workflow_run cascades. Workflow code that an external actor can influence (e.g., through script injection or “pwn requests”) could write to the default-branch cache, and a trusted workflow such as push or schedule would later restore those poisoned entries. This opened up a path to run arbitrary code and exfiltrate production secrets in these more trusted workflows.

To close that path, GitHub now issues a read-only cache token when both of these are true:

• The triggering event is untrusted, meaning someone other than a repository collaborator can trigger the event.
• The workflow execution context and cache scope come from the shared default-branch SHA.

The most common workflow triggers that write to the default-branch cache keep full read-write caching. These triggers are push, schedule, workflow_dispatch, repository_dispatch, delete, registry_package, and page_build. Additionally, any trigger that uses a non-default-branch scope, such as pull_request and release, keeps read-write caching permission.

Who’s affected

This change regresses caching for a small set of untrusted workflows that write to the cache from a default-branch-SHA context. When a write is restricted, actions/cache logs a warning in the run and the job continues without saving. Restores are unaffected.

To keep the benefit of caching in these workflows, you will need to have a separate workflow triggered by an event with read-write cache access such as push which does cache saves. This will enable following workflows with read-only cache access to restore and use the cache.

This change ships to both github.com and GitHub with Data Residency. Check the GitHub Actions cache documentation to learn more, and join the discussion in GitHub Community.

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