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::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. 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 ruby-rack (Ubuntu Pro)Upgrade ruby-rackUpgrade librack-ruby (Ubuntu Pro)Upgrade librack-ruby1.8 (Ubuntu Pro)Upgrade librack-ruby1.9.1 (Ubuntu Pro) | Apr 20, 2026 | Apr 17, 2026 |
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