CVE-2026-34835
Rack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass.
- State
- Published
- Severity
- 4.8 Medium
- Published
- Apr 2, 2026
- Updated
- Apr 2, 2026
- Reserved
- Mar 30, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 4.8 Medium | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N | GitHub_M |
Weaknesses
- CWE-1286 Improper Validation of Syntactic Correctness of Input
Affected Products
| Product | Versions |
|---|---|
rackrack |
|
References
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