CVE-2021-41263: Discourse Rails Multisite

High severity, CVSS 8.8. EPSS: 0.6% chance of exploitation in the next 30 days.

rails_multisite provides multi-db support for Rails applications. In affected versions 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. 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.

Affected products

• Discourse Rails Multisite: before 4.0.0 (fixed in 4.0.0)

Published 2021-11-15. Last modified 2026-06-17.