Auto-set subprocess env scrub when allowed_non_write_users is configured (#1093)

* Auto-set CLAUDE_CODE_SUBPROCESS_ENV_SCRUB when allowed_non_write_users is configured

Sets the env var automatically whenever allowed_non_write_users is
non-empty, so downstream workflows don't need to add it manually.
Updates the input description and docs/security.md to note the behavior.

:house: Remote-Dev: homespace

* Fall back to inherited env when allowed_non_write_users is unset

:house: Remote-Dev: homespace

* Let workflow/job env override the auto-set scrub flag

Env var takes priority so users can opt in/out via CLAUDE_CODE_SUBPROCESS_ENV_SCRUB
at job or workflow level independently of allowed_non_write_users.

:house: Remote-Dev: homespace

Author: OctavianGuzu

action.yml

@@ -32,7 +32,16 @@ inputs:
     required: false
     default: ""
   allowed_non_write_users:
-    description: "Comma-separated list of usernames to allow without write permissions, or '*' to allow all users. Only works when github_token input is provided. WARNING: Use with extreme caution - this bypasses security checks and should only be used for workflows with very limited permissions (e.g., issue labeling)."
+    description: |
+      Comma-separated list of usernames to allow without write permissions, or '*' to allow all users.
+      Only works when github_token input is provided. WARNING: Use with extreme caution - this
+      bypasses security checks and should only be used for workflows with very limited permissions
+      (e.g., issue labeling).
+
+      SECURITY: Processing untrusted content exposes the workflow to prompt injection. When this
+      input is set, Claude does a best-effort scrub of Anthropic, cloud, and GitHub Actions secrets
+      from subprocess environments. This reduces but does not eliminate prompt injection risk -
+      only use for workflows with very limited permissions and validate all outputs.
     required: false
     default: ""
   include_comments_by_actor:
@@ -204,6 +213,7 @@ runs:
         OVERRIDE_GITHUB_TOKEN: ${{ inputs.github_token }}
         ALLOWED_BOTS: ${{ inputs.allowed_bots }}
         ALLOWED_NON_WRITE_USERS: ${{ inputs.allowed_non_write_users }}
+        CLAUDE_CODE_SUBPROCESS_ENV_SCRUB: ${{ env.CLAUDE_CODE_SUBPROCESS_ENV_SCRUB || (inputs.allowed_non_write_users != '' && '1') || '' }}
         INCLUDE_COMMENTS_BY_ACTOR: ${{ inputs.include_comments_by_actor }}
         EXCLUDE_COMMENTS_BY_ACTOR: ${{ inputs.exclude_comments_by_actor }}
         GITHUB_RUN_ID: ${{ github.run_id }}

docs/security.md

@@ -13,6 +13,7 @@
   - Accepts either a comma-separated list of specific usernames or `*` to allow all users
   - **Should be used with extreme caution** as it bypasses the primary security mechanism of this action
   - Is designed for automation workflows where user permissions are already restricted by the workflow's permission scope
+  - When set, Claude does a best-effort scrub of Anthropic, cloud, and GitHub Actions secrets from subprocess environments. This reduces but does not eliminate prompt injection risk — keep workflow permissions minimal and validate all outputs. Set `CLAUDE_CODE_SUBPROCESS_ENV_SCRUB: 0` in your workflow or job `env:` block to opt out.
 - **Token Permissions**: The GitHub app receives only a short-lived token scoped specifically to the repository it's operating in
 - **No Cross-Repository Access**: Each action invocation is limited to the repository where it was triggered
 - **Limited Scope**: The token cannot access other repositories or perform actions beyond the configured permissions