A flaw was found in rubygem-safemode. Compound assignment expressions in sandboxed code are evaluated without mediating method calls through the Jail allow-list. An authenticated attacker who can supply template content can invoke arbitrary no-argument methods on objects exposed to the template renderer without Jail mediation, including destructive operations such as host deletion and disclosure of non-allow-listed object state.
Restrict template edit privileges to trusted administrators until a fixed safemode release is deployed. Where feasible, avoid exposing highly privileged ActiveRecord objects to untrusted template authors.