Summary
EasyAdmin serves all backend requests through a single dashboard route and, for custom actions (Action::linkToRoute() / MenuItem::linkToRoute()), swaps the executed controller based on the routeName query parameter on the kernel.controller event.
That swap happens after Symfony's security firewall has already evaluated accesscontrol against the original dashboard URL, and the routeName value was not validated. As a result, a path-based accesscontrol rule protecting the target route was never evaluated, so a low-privilege backend user could reach a more restricted route by name.
Impact
Any application where accesscontrol (or another path-based Symfony security rule) protects some routes more strictly than the dashboard URL used to reach EasyAdmin. An attacker who can reach a single EasyAdmin URL and knows a target route's name can execute that route's controller, bypassing the path-based rule.
Only path-based protections are bypassed. Routes whose controller enforces its own authorization with #[IsGranted] / denyAccessUnlessGranted() remain protected, because those checks are recomputed against the swapped-in controller.
Patches
Fixed in 4.29.16 and 5.5.1. Before dispatching a custom-action route, EasyAdmin now re-evaluates the target route's accesscontrol rule and denies the request if the current user is not granted access.
Workarounds
Add controller-level authorization (#[IsGranted] / denyAccessUnlessGranted()) to any sensitive route, since controller-level checks are still enforced. Upgrading is the recommended fix.
Credits
Reported by @TungNGo02.