October CMS: Safe Mode Sandbox Bypass via Session Store and Forwarded Builder Calls

Summary

October System provides the system module for October Content Management System. Versions prior to 3.7.17 and 4.2.21 have a vulnerability in the Twig sandbox security policy that allowed a chained bypass when `cms.safe_mode` is enabled. The Laravel session store was exposed to Twig with unrestricted method access, and raw SQL methods reachable through Eloquent's `__call` forwarding were not blocked across the full builder chain. When combined, a backend user with CMS markup editing access could read arbitrary database values via raw SQL expressions and write to the backend authentication session key, forging a backend session as another existing user. The scope of impact is narrow. Safe Mode is a niche feature, primarily used for demo installations and multi-tenant or shared-editor scenarios where untrusted users are deliberately granted access to the CMS markup editor. Standard production deployments do not enable Safe Mode, because under normal October CMS guidance backend access - including markup editing - is restricted to trusted administrators, and direct PHP injection through markup is already possible without Safe Mode in that configuration. This issue only affects sites that meet all of the following conditions: `cms.safe_mode` is enabled (a deliberate opt-in for demos or untrusted-editor scenarios; the site has at least one backend user with CMS markup editing access who is not intended to be trusted as a full administrator; and the site has at least one existing superuser account whose session the lower-privileged user can impersonate. The vulnerability has been patched in v3.7.17 and v4.2.21. The Laravel session store is now wrapped in a proxy that exposes only an explicit subset of read/write methods and rejects writes to reserved session key prefixes (`admin_auth`, `october_auth`, `login_*`, `_token`, and other framework internals). Raw SQL and subquery methods (`selectRaw`, `whereRaw`, `orderByRaw`, `joinSub`, and related) are now blocked on `Query\Builder`, `Eloquent\Builder`, and `Eloquent\Model` so the blocklist is consistent across the `__call` forwarding chain. All sites that enable `cms.safe_mode` are encouraged to upgrade to the latest patched version. A workaround is available. Restrict CMS markup editing access to fully trusted administrators only - the standard October CMS recommendation for any deployment. Note that disabling `cms.safe_mode` is not a workaround; Safe Mode is the boundary this issue affects, and disabling it removes the only sandbox between markup editors and the server.