GHSA-f84q-mgj9-8jfc: 
PHP vulnerability analysis and mitigation

The vulnerability (GHSA-f84q-mgj9-8jfc) is a content moderation access bypass issue in Drupal Core, discovered and disclosed on October 17, 2018. This moderately critical vulnerability affects Drupal versions 8.0.0 through 8.5.8 and 8.6.0 through 8.6.2. The issue was patched in versions 8.5.8 and 8.6.2 (Drupal Advisory, GitHub Advisory).

Under specific conditions, the Drupal content moderation system fails to properly validate user access permissions for certain state transitions. This vulnerability affects the content moderation functionality, particularly in how it handles user permissions for content state changes. The issue required changes to several components including ModerationStateConstraintValidator and StateTransitionValidationInterface, with implications for backwards compatibility (Drupal Advisory).

The vulnerability allows users to bypass access controls in certain conditions, potentially enabling unauthorized users to perform content moderation transitions they shouldn't have access to. Previously, users without explicit access to content moderation transitions were granted implicit access to update content when the state remained unchanged, which created a security gap (Drupal Advisory).

The vulnerability requires specific conditions to be exploited and is rated as moderately critical. The issue primarily affects the content moderation system's access control mechanisms (GitHub Advisory).

Users are advised to upgrade to the patched versions: Drupal 8.5.8 for 8.5.x users or Drupal 8.6.2 for 8.6.x users. The fix includes modifications to user permissions validation, ensuring that access to associated transitions is properly validated for all users, even in scenarios where the content state doesn't change between revisions (Drupal Advisory).