Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Rack | Rack | >= 3.0.0, < 3.1.21 |
Related Weaknesses (CWE)
References
- https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5Vendor AdvisoryExploitMitigation
FAQ
What is CVE-2026-34835?
CVE-2026-34835 is a vulnerability with a CVSS score of 4.8 (MEDIUM). 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 acce...
How severe is CVE-2026-34835?
CVE-2026-34835 has been rated MEDIUM with a CVSS base score of 4.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34835?
Check the references section above for vendor advisories and patch information. Affected products include: Rack Rack.