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

An authenticated backend user with CMS markup editing access could bypass the Safe Mode sandbox to read arbitrary database values and impersonate an existing superuser. This affects sites with cms.safe_mode enabled, a markup editor who is not trusted as a full administrator, and at least one existing superuser account. Disabling Safe Mode does not make untrusted markup editing safe, because it removes the sandbox.

Look for october/system in composer.lock. The listed affected versions are below 3.7.17, or at least 4.0.0 but below 4.2.23. Then check that cms.safe_mode is enabled, that at least one backend user has CMS markup editing access without being trusted as a full administrator, and that an existing superuser account is present. All these conditions must apply. The advisory's patch section names 4.2.21, but its affected range and fixed-version list identify 4.2.23 as the fix for the 4.x branch.

If you cannot upgrade immediately, restrict CMS markup editing access to fully trusted administrators only. Do not disable cms.safe_mode as a workaround: doing so removes the sandbox between markup editors and the server.

A vulnerability was identified 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.

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
• The site has at least one existing superuser account whose session the lower-privileged user can impersonate

Impact

• Arbitrary read access to database tables, including superuser persistence codes from backend_users, via raw SQL expressions reachable through Eloquent\Model, Eloquent\Builder, or any allowlisted class that __call-forwards to a query builder
• Forgery of a backend authentication session by writing to the admin_auth session key from a Twig template, allowing a markup editor to impersonate an existing superuser
• Requires authenticated backend access with CMS markup editing permission AND cms.safe_mode enabled
• Not exploitable when Safe Mode is disabled (direct PHP injection through markup is already possible in that configuration, so Safe Mode is the boundary this issue affects)

Patches

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.

Workarounds

If upgrading immediately is not possible:

• 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

References

• Reported by r00tn0b0dy