Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21 and 3.2.0 to before 3.2.6, Rack::Utils.forwarded_values parses the RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values. Because quoted values may legally contain semicolons, a header can be interpreted by Rack as multiple Forwarded directives rather than as a single quoted for value. In deployments where an upstream proxy, WAF, or intermediary validates or preserves quoted Forwarded values differently, this discrepancy can allow an attacker to smuggle host, proto, for, or by parameters through a single header value. This issue has been patched in versions 3.1.21 and 3.2.6.
CVSS Details
- CVSS 3.1 Base Score: 6.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Debian | — | Upgrade ruby-rack | Sep 21, 2026 | Apr 2, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Apr 2, 2026 |
| Ubuntu | — | Upgrade librack-ruby1.8 (Ubuntu Pro)Upgrade ruby-rack (Ubuntu Pro)Upgrade librack-ruby (Ubuntu Pro)Upgrade librack-ruby1.9.1 (Ubuntu Pro)Upgrade ruby-rack | Apr 20, 2026 | Apr 17, 2026 |
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