Rails Multisite secure/signed cookies share secrets between sites in a multi-site application

Impact

This vulnerability impacts any Rails applications using rails_multisite alongside Rails’ signed/encrypted cookies. Depending on how the application makes use of these cookies, it may be possible for an attacker to re-use cookies on different ‘sites’ within a multi-site Rails application.

Patches

The issue has been patched in v4 of the rails_multisite gem. Note that this upgrade will invalidate all previous signed/encrypted cookies. The impact of this invalidation will vary based on the application architecture.